Microporous filter media, filtration systems containing same, and methods of making and using

ABSTRACT

The invention is directed to a microbiological interception enhanced filter medium, preferably having an adsorbent prefilter located upstream from the filter medium. Preferably, the prefilter is adapted to remove natural organic matter in an influent prior to the influent contacting the microbiological interception enhanced filter medium, thereby preventing loss of charge on the filter medium. The microbiological interception enhanced filter medium is most preferably comprised of fibrillated cellulose fibers, in particular, lyocell fibers. At least a portion of the surface of the at least some of the fibers have formed thereon a microbiological interception enhancing agent comprising a cationic metal complex. A filter medium of the present invention provides greater than about 4 log viral interception, and greater than about 6 log bacterial interception.

[0001] This application claims priority from U.S. ProvisionalApplication Serial No. 60/354,062 filed on Jan. 31, 2002.

[0002] The present invention is directed to filter media havingmicrobiological interception capability, filtration systems containingsuch filter media, and methods of making and using same.

[0003] Modern consumer water filters often provide “health claims”including reduction of particulates, heavy metals, toxic organicchemicals, and select microbiological threats. These filtration systemshave been able to intercept microorganisms such as Cryptosporidium andGiardia using roughly 1.0 micron structures. However, in order toprovide microbiological interception of even smaller microbiologicalthreats such as viruses, a filter medium having a sub-micron microporousstructure is required. Prior art filtration systems often attempt toachieve broad microbiological interception using filter media withinsufficiently small pore size and with poor physical integrity. Thebalance between the necessary pore structure required for successfulmicrobiological interception and satisfactory filter performance has notbeen achieved. In addition, prior art systems did not provided devicescapable of operating in the presence of “interferences” consisting ofsubstances that cause a loss of filtration performance.

SUMMARY OF THE INVENTION

[0004] The present invention is directed to, in a first aspect, a filtermedium comprising: a microporous structure having a mean flow path ofless than or equal to about 1 micron; and a microbiological interceptionenhancing agent comprising a cationic metal complex capable of impartinga positive charge on at least a portion of the microporous structure.

[0005] In another aspect, the present invention is directed to acomposite filter medium comprising: as adsorbent prefilter havingimmobilized therein a material capable of removing charge-reducingcontaminants; a microporous structure, disposed downstream from theadsorbent layer, comprising a plurality of nanofibers, the microporousstructure having a mean flow path of less than about 0.6 micron; and amicrobiological interception enhancing agent comprising asilver-cationic material-halide complex having a high charge density,coated on at least a portion of a surface of at least some of theplurality of fibers of the fiber matrix.

[0006] In yet another aspect, the present invention is directed to afilter system comprising: a granular bed of particles capable ofremoving charge-reducing contaminants; a microporous structure, disposeddownstream from the granular bed, having a mean flow path of less thanabout 0.6 micron; and a microbiological interception enhancing agentcomprising a silver-cationic material-halide complex having a highcharge density, coated on at least a portion of a surface of themicroporous structure.

[0007] In still yet another aspect, the present invention is directed toa filter system comprising: a solid composite block comprising amaterial capable of removing charge-reducing contaminants; a microporousstructure, disposed downstream from the block, having a mean flow pathof less than about 2.0 microns; and a microbiological interceptionenhancing agent comprising a silver-cationic material-halide complexhaving a high charge density, coated on at least a portion of a surfaceof the microporous structure.

[0008] In still yet another aspect, the present invention is directed toa process of making a filter medium comprising the steps of: providing amicroporous structure having a mean flow path of less than about 1micron; and coating at least a portion of the microporous structure witha microbiological interception enhancing agent, the microbiologicalinterception enhancing agent comprising a cationic metal complex capableof imparting a positive charge on at least a portion of the microporousstructure.

[0009] In a further aspect, the present invention is directed to aprocess for making a filter medium comprising the steps of: providing aplurality of nanofibers; coating at least a portion of a surface of atleast some of the plurality of nanofibers with a microbiologicalinterception enhancing agent, the microbiological intercepting agentcomprising a cationic metal complex; and forming the fibers into amicroporous structure having a mean flow path of less than about 1micron.

[0010] In still a further aspect, the present invention is directed to aprocess for making a filter medium comprising the steps of: providing aplurality of polymer nanofibers; coating at least a portion of a surfaceof at least some of the plurality of polymer nanofibers with amicrobiological interception enhancing agent, the microbiologicalintercepting agent comprising a cationic metal complex; and forming amicroporous structure having a mean flow path of less than about 1micron.

[0011] In still a further aspect, the present invention is directed to aprocess for making a filter medium comprising the steps of: providing aplurality of cellulose nanofibers; coating at least a portion of asurface of at least some of the plurality of cellulose fibers with amicrobiological interception enhancing agent, the microbiologicalintercepting agent comprising a cationic metal complex; and forming amicroporous structure having a mean flow path of less than about 1micron.

[0012] In still yet a further aspect, the present invention is directedto a process of making a filter medium comprising the steps of:providing a membrane having a mean flow path of less than about 1micron; and coating at least a portion of the membrane with amicrobiological interception enhancing agent, the microbiologicalinterception enhancing agent comprising a cationic metal complex capableof imparting a positive charge on at least a portion of the membrane.

[0013] In still yet a further aspect, the present invention is directedto a process for making a filter medium comprising the steps of:providing a plurality of nanofibers; coating at least a portion of asurface of at least some of the plurality of the nanofibers with amicrobiological interception enhancing agent, the microbiologicalintercepting agent comprising a silver-amine-halide complex having amedium to high charge density and a molecular weight greater than 5000Daltons; and forming a microporous structure having a mean flow path ofless than or about 0.6 microns.

[0014] In still yet a further aspect, the present invention is directedto a process for making a filter system comprising the steps of:providing an adsorbent prefilter comprising a material capable ofremoving charge-reducing contaminants from an influent, wherein thematerial is immobilized into a solid composite block; providing aplurality of nanofibers; coating at least a portion of a surface of atleast some of the plurality of the nanofibers with a microbiologicalinterception enhancing agent, the microbiological intercepting agentcomprising a silver-amine-halide complex having a medium to high chargedensity and a molecular weight greater than 5000 Daltons; and forming amicroporous structure having a mean flow path of less than or about 0.6microns.

[0015] In still yet a further aspect, the present invention is directedto a method of removing microbiological contaminants in a fluidcomprising the steps of: providing a filter medium having a microporousstructure having a mean flow path of less than about 1 micron, themicroporous structure having coated on at least a portion thereof amicrobiological interception enhancing agent comprising a cationic metalcomplex wherein the cationic material has a medium to high chargedensity and a molecular weight greater than about 5000 Daltons;contacting the fluid to the filter medium for greater than about 3seconds; and obtaining at least about 6 log reduction of microbiologicalcontaminants smaller than the mean flow path of the filter medium, thatpass through the filter medium.

[0016] In still yet a further aspect, the present invention is directedto a gravity-flow filtration system for treating, storing, anddispensing fluids comprising: a first reservoir for holding a fluid tobe filtered; a filter medium in fluid communication with the firstreservoir, the filter medium comprising a microporous structure with amean flow path of less than about 1 micron, and wherein the filtermedium is so treated as to provide at least about 4 log reduction ofmicrobiological contaminants smaller than the mean flow path of thefilter medium; and a second reservoir in fluid communication with thefilter medium for collecting a filtered fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The features of the invention believed to be novel and theelements characteristic of the invention are set forth withparticularity in the appended claims. The figures are for illustrationpurposes only and are not drawn to scale. The invention itself, however,both as to organization and method of operation, may best be understoodby reference to the description of the preferred embodiment(s) thatfollows taken in conjunction with the accompanying drawings in that:

[0018]FIG. 1 is a side plan view of a filter incorporating the filtermedia of the present invention.

[0019]FIG. 2 is a cross sectional view of the filter of FIG. 1 taken atlines 2-2.

[0020]FIG. 3 is a front plan view of an exemplary gravity flowfiltration system of the present invention.

[0021]FIG. 4 is a perspective view of another exemplary gravity flowfiltration system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1 to 4 of the drawings in thatlike numerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

[0023] Definitions

[0024] As used herein, “absorbent” shall mean any material that iscapable of absorbing impurities primarily by drawing the impurities intoits inner structure.

[0025] As used herein, “adsorbent” shall mean any material that iscapable of adsorbing impurities primarily by physical adsorption to itssurface.

[0026] As used herein, “adsorbent filter medium” or “adsorbentprefiltration medium” shall mean a filter medium made with an adsorbentsuch as, for example, activated carbon. Exemplary of an adsorbent filtermedium is PLEKX®, commercially available from KX Industries, L. P. ofOrange, Conn.

[0027] As used herein, “binder” shall mean a material used principallyto hold other materials together.

[0028] As used herein, “Canadian Standard Freeness” or “CSF” shall meana value for the freeness or drainage rate of pulp as measured by therate that a suspension of pulp may be drained. This methodology is wellknown to one having skill in the paper making arts.

[0029] As used herein, “composite filter medium” shall mean a filtermedium that combines a prefilter, an adsorbent prefiltration medium, andthe microbiological interception enhanced filter medium of the presentinvention, into a single composite structure. In some cases, theprefilter may be absent or its function assumed by the adsorbentprefiltration medium.

[0030] As used herein, “contaminant reduction” shall mean attenuation ofan impurity in a fluid that is intercepted, removed, or renderedinactive, chemically or biologically, in order to render the fluid saferas, for example for human use, or more useful, as in industrialapplications.

[0031] As used herein, “fiber” shall mean a solid that is characterizedby a high aspect ratio of length to diameter of, for example, severalhundred to one. Any discussion of fibers includes whiskers.

[0032] As used herein, “filter medium” shall mean a material thatperforms fluid filtration.

[0033] As used herein, “fluid” shall mean a liquid, gas, or combinationthereof.

[0034] As used herein, “forming” shall mean converting a loose,unstructured substance into a cohesive, uniform structure. For example,the conversion of loose fibers into a paper.

[0035] As used herein, “intercept” or “interception” are taken to meaninterfering with, or stopping the passage of, so as to affect, remove,inactivate or influence.

[0036] As used herein, “log reduction value” or “LRV” shall mean thelog₁₀ of the number of organisms in the influent divided by the numberof organisms in the effluent of a filter.

[0037] As used herein, “membrane” shall mean a porous medium wherein thestructure is a single continuous solid phase with a continuous porestructure.

[0038] As used herein, “microbiological interception enhanced filtermedium” shall mean a filter medium having a microporous structure whereat least a portion of its surface is treated with a microbiologicalinterception enhancing agent.

[0039] As used herein, “microorganism” shall mean any living organismthat may be suspended in a fluid, including but not limited to bacteria,viruses, fungi, protozoa, and reproductive forms thereof including cystsand spores.

[0040] As used herein, “microporous structure” shall mean a structurethat has a mean flow path less than about 2.0 microns, and often lessthan about 1.0 micron.

[0041] As used herein, “nanofiber” shall mean a fiber having a diameterless than about 3.0 millimeters.

[0042] As used herein, “natural organic matter” or “NOM” shall meanorganic matter often found in potable or non-potable water, a portion ofwhich reduces or inhibits the zeta potential of a positively chargedfilter medium. Exemplary of NOM are polyanionic acids such as, but notlimited to, humic acid and fulvic acid.

[0043] As used herein, “nonwoven” means a web or fabric or other mediumhaving a structure of individual fibers that are interlaid, but not in ahighly organized manner as in a knitted or woven fabric. Nonwoven websgenerally may be prepared by methods that are well known in the art.Examples of such processes include, but are not limited to, and by wayof illustration only, meltblowing, spunbonding, carding, and air laying.

[0044] As used herein, “paper” or “paper-like” shall mean a generallyflat, fibrous layer or mat of material formed by a wet laid process.

[0045] As used herein, “particle” shall mean a solid having a size rangefrom the colloidal to macroscopic, and with no specific limitation onshape, but generally of a limited length to width ratio.

[0046] As used herein, “prefilter” shall mean a filter medium generallylocated upstream from other filtration layers, structures or devices andcapable of reducing particulate contaminants prior to the influentcontacting subsequent filtration layers, structures or devices.

[0047] As used herein, “sheet” shall mean a roughly two-dimensionalstructure having a length and a width that are significantly greaterthan its thickness.

[0048] As used herein, “whisker” shall mean a filament having a limitedaspect ratio and intermediate between the aspect ratio of a particle anda fiber. Any discussion of fibers includes whiskers.

[0049] The Microbiological Interception Enhanced Filter Medium

[0050] A filter medium of the present invention includes a microporousstructure that provides microbiological interception capability using acombination of an appropriate pore structure and a chemical treatment.The microporous structure comprises any material that is capable ofhaving a mean flow path of less than about 2.0 microns. Preferably, themicroporous structure comprises nanofibers formed into a nonwoven orpaper-like structure, but may include whiskers, or be a membrane. Thetight pore structure of the microbiological interception enhanced filtermedium of the present invention provides short diffusion distances fromthe fluid to the surface of the filter medium. The chemical treatmentprocess used to treat the surface of the microporous structure utilizesa synergistic interaction between a cationic material and a biologicallyactive metal, that when combined, provide broad-spectrum reduction ofmicrobiological contaminants on contact. The charge provided by thecationic material to the filter medium aids in electro-kineticinterception of microbiological contaminants, while the tight porestructure provides a short diffusion path and, therefore, rapiddiffusion kinetics of contaminants in a flowing fluid to the surface ofthe microporous structure. The microporous structure also providessupplemental direct mechanical interception of microbiologicalcontaminants. Due to the dominant role of diffusion for the interceptionof extremely small particles, there is a direct correlation between thelog reduction value of viral particles and the contact time of theinfluent within the filter medium, rather than a dependence upon thethickness of the filter medium.

[0051] Characteristics of the Microbiological Interception EnhancedFilter Medium

[0052] In order to provide full microbiological interception capability,the microbiological interception enhanced filter medium of the presentinvention has a mean flow path of less than about 2 microns, andpreferably less than or equal to about 1 micron, and more preferablyless than or equal to about 0.6 microns. The volume of themicrobiological interception enhanced filter medium of the presentinvention compared to the flow rate of fluid through the filter mediummust be sufficient to provide a contact time adequate for thecontaminants to diffuse to the surface of the filter medium. To provideenhanced electro-kinetic interception of microorganisms, of which themajority are negatively charged, under most conditions, themicrobiological interception enhanced filter medium has a positive zetapotential generally greater than about +10 millivolts at pH values ofabout 6 to about 7, and retains a net positive zeta potential at pHvalues of about 9 or greater.

[0053] Natural organic matter (NOM), such as polyanionic acids, i.e.,humic acid or fulvic acid, that may reduce or remove the charge on themicrobiological interception enhanced filter medium, is preferablyprevented from contacting the charged microporous structure through theuse of an adsorbent prefilter that substantially removes the NOM. Whenused in the context of a gravity-flow water filtration system, it ispreferable that the microbiological interception enhanced filter mediumbe made with hydrophilic materials to provide good, spontaneouswettability. Alternatively, in other applications, the microbiologicalinterception enhanced filter medium may be treated to provide either ahydrophilic or hydrophobic characteristic as needed. It is possible thatthe microbiological interception enhanced filter medium can have bothpositively and negatively charged and uncharged regions, and/orhydrophilic and hydrophobic regions. For example, the negatively chargedregions can be used to enhance the interception of less commonpositively charged contaminants and uncharged hydrophobic regions can beused to provide enhanced interception of contaminants that are attractedto hydrophobic surfaces.

[0054] The Fibers/Whiskers or Particulate Ingredients

[0055] The microbiological interception enhanced filter medium of thepresent invention includes a microporous structure that may include aplurality of nanofibers, including whiskers or micro-particulateingredients, of organic and inorganic materials including, but notlimited to, polymers, ion-exchange resins, engineered resins, ceramics,cellulose, rayon, ramie, wool, silk, glass, metal, activated alumina,carbon or activated carbon, silica, zeolites, diatomaceous earth,activated bauxite, fuller's earth, calcium hydroxyappatite, otheradsorbent materials, or combinations thereof. Combinations of organicand inorganic fibers and/or whiskers or micro-particules arecontemplated and within the scope of the invention as for example,glass, ceramic, or metal fibers and polymeric fibers may be usedtogether with very small particles incorporated into the microporousstructure.

[0056] When produced by a wet laid process from nanofibers such ascellulose or polymer fibers, such fibers should also have a CanadianStandard Freeness of less than or equal to about 100, and mostpreferably less than or equal to about 45. Preferably, a significantportion of the fibers should have a diameter less than or equal to about1000 nanometers, more preferably less than or equal to about 400nanometers, and fibers less than or equal to about 250 nanometers indiameter are most preferred. It is preferable to chop the fibers to alength of about 1 millimeter to about 8 millimeters, preferably about 2millimeters to about 6 millimeters, and more preferably about 3millimeters to about 4 millimeters. Fibrillated fibers are mostpreferred due to their exceptionally fine dimensions and potentially lowcost.

[0057] Preferably, fibrillated synthetic cellulose fibers, processed inaccordance with the present invention, can produce an ultra-fine,hydrophilic microporous structure for use as the microbiologicalinterception enhanced filter medium of the present invention. Suchfibrillated cellulose fibers can be made by direct dissolution andspinning of wood pulp in an organic solvent, such as an amine oxide, andare known as lyocell fibers. Lyocell fibers have the advantage of beingproduced in a consistent, uniform manner, thus yielding reproducibleresults, which may not be the case for, for example, natural cellulosefibers. Further, the fibrils of lyocell are often curled. The curlsprovide a significant amount of fiber entanglement, resulting in afinished filter medium with high dry strength and significant residualwet strength. Furthermore, the fibrillated lyocell fibers may beproduced in large quantities using equipment of modest capital cost. Itwill be understood that fibers other than cellulose may be fibrillatedto produce extremely fine fibrils, such as for example, artificialfibers, in particular, acrylic or nylon fibers, or other naturalcellulosic materials. Combinations of fibrillated and non-fibrillatedfibers may be used in the microporous structure.

[0058] Membranes

[0059] The microbiological interception enhanced filter medium of thepresent invention can comprise a membrane of organic or inorganiccomposition including, but not limited to, polymers, ion-exchangeresins, engineered resins, ceramics, cellulose, rayon, ramie, wool,silk, glass, metal, activated alumina, activated carbon, silica,zeolites, diatomaceous earth, activated bauxite, fuller's earth, calciumhydroxyappatite, titanates and other materials, or combinations thereof.Combinations of organic and inorganic materials are contemplated andwithin the scope of the invention. Such membranes may be made usingmethods known to one of skill in the art.

[0060] The Microbiological Interception Enhancing Agent

[0061] The nanofibers or membrane that make up the microporous structureare chemically treated with a microbiological interception enhancingagent capable of creating a positive charge on the microbiologicalinterception enhanced filter medium. A cationic metal complex is formedon at least a portion of the surface of at least some of the fibers orthe membrane by treating the fibers or membrane with a cationicmaterial. The cationic material may be a small charged molecule or alinear or branched polymer having positively charged atoms along thelength of the polymer chain.

[0062] If the cationic material is a polymer, the charge density ispreferably greater than about 1 charged atom per about every 20Angstroms, preferably greater than about 1 charged atom per about every12 Angstroms, and more preferably greater than about 1 charged atom perabout every 10 Angstroms of molecular length. The higher the chargedensity on the cationic material, the higher the concentration of thecounter ion associated therewith. A high concentration of an appropriatecounter ion can be used to drive the precipitation of a cationic metalcomplex. The cationic material should consistently provide a highlypositively charged surface to the microporous structure as determined bya streaming or zeta potential analyzer, whether in a high or low pHenvironment. Zeta or streaming potentials of the microporous structureafter treatment with a high molecular weight charged polymer can begreater than about +10 millivolts, and often up to about +23 millivoltsat a substantially neutral pH.

[0063] The cationic material includes, but is not limited to,quaternized amines, quaternized amides, quaternary ammonium salts,quaternized imides, benzalkonium compounds, biguanides, cationicaminosilicon compounds, cationic cellulose derivatives, cationicstarches, quaternized polyglycol amine condensates, quaternized collagenpolypeptides, cationic chitin derivatives, cationic guar gum, colloidssuch as cationic melamine-formaldehyde acid colloids, inorganic treatedsilica colloids, polyamide-epichlorohydrin resin, cationic acrylamides,polymers and copolymers thereof, combinations thereof, and the like.Charged molecules useful for this application can be small moleculeswith a single charged unit and capable of being attached to at least aportion of the microporous structure. The cationic material preferablyhas one or more counter ions associated therewith which, when exposed toa biologically active metal salt solution, cause preferentialprecipitation of the metal in proximity to the cationic surface to forma cationic metal precipitate.

[0064] Exemplary of amines may be pyrroles, epichlorohydrin derivedamines, polymers thereof, and the like. Exemplary of amides may be thosepolyamides disclosed in International Patent Application No. WO01/07090, and the like. Exemplary of quaternary ammonium salts may behomopolymers of diallyl dimethyl ammonium halide, epichlorohydrinderived polyquaternary amine polymers, quaternary ammonium salts derivedfrom diamines and dihalides such as those disclosed in U.S. Pat. Nos.2,261,002, 2,271,378, 2,388,614, and 2,454,547, all of which areincorporated by reference, and in International Patent Application No.WO 97/23594, also incorporated by reference,polyhexamethylenedimethylammonium bromide, and the like. The cationicmaterial may be chemically bonded, adsorbed, or crosslinked to itself orto the fiber or membrane.

[0065] Furthermore, other materials suitable for use as the cationicmaterial include BIOSHIELD® available from BioShield Technologies, Inc.,Norcross, Ga. BIOSHIELD® is an organosilane product includingapproximately 5% by weight octadecylaminodimethyltrimethoxysilylpropylammonium chloride and less than 3% chloropropyltrimethoxysilane. Anothermaterial that may be used is SURFACINE®, available from SurfacineDevelopment Company LLC, Tyngsboro, Mass. SURFACINE® comprises athree-dimensional polymeric network obtained by reactingpoly(hexamethylenebiguanide) (PHMB) with4,4′-methlyene-bis-N,N-diglycidylaniline (MBGDA), a crosslinking agent,to covalently bond the PHMB to a polymeric surface. Silver, in the formof silver iodide, is introduced into the network, and is trapped assubmicron-sized particles. The combination is an effective biocide,which may be used in the present invention. Depending upon the fiber andmembrane material, the MBGDA may or may not crosslink the PHMB to thefiber or the membrane.

[0066] The cationic material is exposed to a biologically active metalsalt solution such that the cationic metal complex precipitates onto atleast a portion of the surface of at least some of the fibers or themembrane. For this purpose, the metals that are biologically active arepreferred. Such biologically active metals include, but are not limitedto, silver, copper, zinc, cadmium, mercury, antimony, gold, aluminum,platinum, palladium, and combinations thereof. Most preferred are silverand copper. The biologically active metal salt solution is preferablyselected such that the metal and the counter ion of the cationicmaterial are substantially insoluble in an aqueous environment to driveprecipitation of the cationic metal complex.

[0067] A particularly useful microbiological interception enhancingagent is a cationic silver-amine-halide complex. The cationic amine ispreferably a homopolymer of diallyl dimethyl ammonium halide having amolecular weight of about 400,000 Daltons or other quaternary ammoniumsalts having a similar charge density and molecular weight. Ahomopolymer of diallyl dimethyl ammonium chloride useful in the presentinvention is commercially available from Nalco Chemical Company ofNaperville, Ill., under the tradename MERQUAT® 100. The chloride counterion may be replaced with a bromide or iodide counter ion. When contactedwith a silver nitrate solution, the silver-amine halide complexprecipitates on at least a portion of the fibers or membrane of themicroporous structure of the filter medium.

[0068] The pH of the surrounding solution does affect the zeta potentialof the microbiological interception enhanced filter medium of thepresent invention. An acidic pH will increase the charge on the filtermedium while a basic pH will decrease the charge on the filter medium.Under pH conditions typically encountered in potable water, themicrobiological interception enhanced filter medium does retain aminimum positive charge and only at very high pH values does the chargedecline below zero millivolts. Exposure to NOM, such as polyanionicacids, will decrease the zeta potential of the microbiologicalinterception enhanced filter medium. This will diminish itsmicrobiological interception capabilities. Therefore, in applicationswhere high levels of NOM are present, an adsorbent prefilter capable ofremoving the NOM extends the useful life of the microbiologicalinterception enhanced filter medium.

[0069] Methods of Making the Microbiological Interception EnhancedFilter Medium

[0070] The microbiological interception enhanced filter medium may bemade in accordance with processes known to one of skill in the art. Drylaid processes include spun bonding, electrospinning, spinningislands-in-sea processes, fibrillated films, melt blowing, and other drylaid processes known to one of skill in the art. An exemplary dry laidprocess starts with staple fibers, which can be separated by cardinginto individual fibers and are then laid together to a desired thicknessby an aerodynamic or hydrodynamic process to form an unbonded fibersheet. The unbonded fibers can then be subjected to hydraulic jets toboth fibrillate and hydroentangle the fibers. A similar process can beperformed on certain plastic films that when exposed to high pressurejets of water, are converted into webs of fibrillated fibers.

[0071] In a preferred wet laid process, a fiber tow is chopped to aspecific length, usually in the range of about 1 millimeter to about 8millimeters, and in particular in the range of about 3 millimeters toabout 4 millimeters. The chopped fibers are fibrillated in a devicehaving characteristics similar to a blender, or on a large scale, inmachines commonly referred to as a “hi-low”, a “beater” or a “refiner”.The fiber is subjected to repetitive stresses, while further choppingand the reduction of fiber length is minimized. As the fibers undergothese stresses, the fibers split as a result of weaknesses betweenamorphous and crystalline regions and the Canadian Standard Freeness(CSF), which is determined by a method well known in the art, begins todecline. Samples of the resulting pulp can be removed at intervals, andthe CSF used as an indirect measure of the extent of fibrillation. Whilethe CSF value is slightly responsive to fiber length, it is stronglyresponsive to the degree of fiber fibrillation. Thus, the CSF, which isa measure of how easily water may be removed from the pulp, is asuitable means of monitoring the degree of fiber fibrillation. If thesurface area is very high, then very little water will be drained fromthe pulp in a given amount of time and the CSF value will becomeprogressively lower as the fibers fibrillate more extensively. Thefibrillated fiber of a given CSF value can be directly used forproducing paper or dewatered on a variety of different devices,including a dewatering press or belt, to produce a dewatered pulp. Thedewatered pulp can be subsequently used to make a wet-laid paper.Generally, for application in the present invention, a pulp with a CSFof below 100 is used, and preferably, the CSF should be less than orequal to about 45.

[0072] The pulp is treated with a cationic material in such a manner asto allow the cationic material to coat at least a portion of the surfaceof at least some of the fibers thereby imparting a charge on the fibers.Methods of applying the cationic material to the fibers are known in theart and include, but are not limited to, spray, dip, or submergencecoating to cause adsorption, chemical reaction or crosslinking of thecationic material to the surface of the fibers. The treated pulp is thenrinsed in reverse osmosis/deionized (RO/DI) water, partially dewatered,usually under vacuum, to produce a wet lap that can then be exposed to abiologically active metal salt solution. The use of nearly ion-freerinse water causes the counter-ions associated with the cationicmaterial to be drawn tightly against the treated fiber surface and toeliminate unwanted ions that may cause uncontrolled precipitation of thebiologically active metal into sites remote from the cationic surface.

[0073] The metal salt solution is infiltrated into the fibers to allowprecipitation of the cationic metal complex on a surface of at least aportion of the fibers. The precipitation accurately deposits a metalcolloid adjacent to the cationic coating because the counter-ionassociated with this coating reacts with the applied metal salt to formcolloidal particles. After sufficient exposure to the biologicallyactive metal salt solution, the fibers can be rinsed and excess water isremoved. Alternatively, the fibers can be directly sent to pulppreparation systems to create a furnish suitable for paper making.

[0074] When silver nitrate is used as the metal salt solution, thepresence of precipitated silver can be confirmed by using a KratosEDX-700/800 X-ray fluorescence spectrometer available from KratosAnalytical, a Shimadzu Group Company, Japan.

[0075] The microbiological interception enhanced filter mediumcomprising a membrane may be made in accordance with processes known toone of skill in the art. Raw material for the membrane may be treatedprior to forming the membrane or the cationic material may be applied tothe membrane material using known methods in the art and similar tothose used to treat the fiber surfaces.

[0076] Additives

[0077] The strength of the wet laid fiber sheet, especially when wet,may be improved with the addition of various additives. It is well knownin the art that the addition of epoxy or acrylic or other resins to thepaper making process can provide enhanced wet strength, but thesewater-dispersed resins often cause lower permeability to the finalproduct, especially as fiber size becomes very small. Although theseresins and resin systems can be used in the current invention, it ispreferable to use thermoplastic or thermoset materials known in the art,and in either powder, particulate or fiber form.

[0078] Useful binder materials include, but are not limited to,polyolefins, polyvinyl halides, polyvinyl esters, polyvinyl ethers,polyvinyl sulfates, polyvinyl phosphates, polyvinyl amines, polyamides,polyimides, polyoxidiazoles, polytriazols, polycarbodiimides,polysulfones, polycarbonates, polyethers, polyarylene oxides,polyesters, polyarylates, phenol-formaldehyde resins,melamine-formaldehyde resins, formaldehyde-ureas, ethyl-vinyl acetatecopolymers, co-polymers and block interpolymers thereof, andcombinations thereof. Variations of the above materials and other usefulpolymers include the substitution of groups such as hydroxyl, halogen,lower alkyl groups, lower alkoxy groups, monocyclic aryl groups, and thelike. Other potentially applicable materials include polymers such aspolystyrenes and acrylonitrile-styrene copolymers, styrene-butadienecopolymers, and other non-crystalline or amorphous polymers andstructures.

[0079] A more detailed list of binder materials that may be useful inthe present invention include end-capped polyacetals, such aspoly(oxymethylene) or polyformaldehyde, poly(trichloroacetaldehyde),poly(n-valeraldehyde), poly(acetaldehyde), and poly(propionaldehyde);acrylic polymers, such as polyacrylamide, poly(acrylic acid),poly(methacrylic acid), poly(ethyl acrylate), and poly(methylmethacrylate); fluorocarbon polymers, such as poly(tetrafluoroethylene),perfluorinated ethylene-propylene copolymers,ethylene-tetrafluoroethylene copolymers, poly(chlorotrifluoroethylene),ethylene-chlorotrifluoroethylene copolymers, poly(vinylidene fluoride),and poly(vinyl fluoride); polyamides, such as poly(6-aminocaproic acid)or poly(e-caprolactam), poly(hexamethylene adipamide),poly(hexamethylene sebacamide), and poly(11-aminoundecanoic acid);polyaramides, such as poly(imino-1,3-phenyleneiminoisophthaloyl) orpoly(m-phenylene isophthalamide); parylenes, such as poly-2-xylylene,and poly(chloro-1-xylylene); polyaryl ethers, such aspoly(oxy-2,6-dimethyl-1,4-phenylene) or poly(p-phenylene oxide);polyaryl sulfones, such aspoly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyl-eneisopropylidene-1,4-phenylene),andpoly(sulfonyl-1,4-phenylene-oxy-1,4-phenylenesulfonyl4,4′-biphenylene);polycarbonates, such as poly-(bisphenol A) orpoly(carbonyldioxy-1,4-phenyleneisopropylidene-1,4-phenylene);polyesters, such as poly(ethylene terephthalate), poly(tetramethyleneterephthalate), and poly(cyclohexyl-ene-1,4-dimethylene terephthalate)or poly(oxymethylene-1,4-cyclohexylenemethyleneoxyterephthaloyl);polyaryl sulfides, such as poly(p-phenylene sulfide) orpoly(thio-1,4-phenylene); polyimides, such aspoly(pyromellitimido-1,4-phenylene); polyolefins, such as polyethylene,polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene),poly(2-pentene), poly(3-methyl-1-pentene), and poly(4-methyl-1-pentene);vinyl polymers, such as poly(vinyl acetate), poly(vinylidene chloride),and poly(vinyl chloride); diene polymers, such as1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, andpolychloroprene; polystyrenes; and copolymers of the foregoing, such asacrylonitrilebutadiene-styrene (ABS) copolymers. Polyolefins that may beuseful include polyethylene, linear low density polyethylene,polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene),poly(2-pentene), poly(3-methyl-1-pentene), poly(4-methyl-1-pentene), andthe like.

[0080] A range of binder fibers, including polyethylene, polypropylene,acrylic, or polyester-polypropylene or polypropylene-polyethylenebi-component fibers, or others can be used. Certain types of treatedpolyethylene fibers, when properly treated, as described below, areoptimal, and have the additional benefit of not significantlyinterfering with the hydrophilic nature of the resulting filter mediumwhen used in modest volumes. Preferred fiber binder materials mayinclude FYBREL® synthetic fibers and/or SHORT STUFF® EST-8, both ofwhich are polyolefin based. FYBREL® is a polyolefin based synthetic pulpthat is a highly fibrillated fiber and is commercially available fromMitsui Chemical Company, Japan. FYBREL® has excellent thermalmoldability and provides a smooth surface to the filter medium. SHORTSTUFF® EST-8 is commercially available from MiniFibers, Inc.,Pittsburgh, Pa., and is a highly fibrillated, high density polyethylene.

[0081] Preferably, the binder material is present in an amount of about1% to about 10% by weight, more preferably about 3% to about 6%, andmost preferably about 5%. It is preferable that the binder material havea softening point that is significantly lower than a softening point ofthe nanofiber material so that the filter medium can be heated toactivate the binder material, while the microporous structure does notmelt and thereby lose porosity.

[0082] One or more additives either in a particulate, fiber, whisker, orpowder form may also be mixed with the nanofibers or incorporated intothe membrane to aid in adsorption of other contaminants or participatein the formation of the microporous structure and interception ofmicrobiological contaminants. Useful additives may include, but are notlimited to, metallic particles, activated alumina, activated carbon,silica, polymeric powders and fibers, glass beads or fibers, cellulosefibers, ion-exchange resins, engineered resins, ceramics, zeolites,diatomaceous earth, activated bauxite, fuller's earth, calcium sulfate,other adsorbent materials such as super adsorbent polymers (SAPs), orcombinations thereof. The additives can also be chemically treated toimpart microbiological interception capabilities depending upon theparticular application. Such additives are preferably present in asufficient amount such that the fluid flow in the resultant filtermedium is not substantially impeded when used in filtrationapplications. The amount of additives is dependent upon the particularuse of the filtration system.

[0083] Exemplary of a wet laid process includes mixing a pulp of 45 CSFfibrillated lyocell fibers with 5% EST-8 binder fibers and dispersingthe pulp and binder fibers in deionized water with mixing in a blenderto form a furnish with about 1% to about 2% consistency. To this mixtureis added about 3% by weight of MERQUAT® 100, which is briefly dispersedinto the dilute pulp furnish. The cationic material remains in contactwith the pulp for about 4 to about 12 hours until a significant portionhas been adsorbed onto at least a portion of the fibers to impart andmaintain a positive zeta potential on the fibers. Within about eighthours at room temperature, sufficient MERQUAT® is adsorbed to provide apositive zeta potential on the fibers that is greater than about +10millivolts. Next, this pulp is partially dewatered under vacuum andrinsed with deionized water to form a wet lap. A metal salt solution,such as, for example, silver nitrate, in an amount equal to 0.5% byweight of the dry nanofibers, is prepared with deionized water, anduniformly poured over the sheet and allowed to stand for a short time toallow precipitation of the biologically active metal with at least aportion of the counter ion associated with the cationic material.Thereafter, the fibers can be directly used in the production of wetlaid filter medium.

[0084] Filtration Systems Utilizing the Microbiological InterceptionEnhanced Filter Medium

[0085] Many types of filtration systems incorporating the current filtermedium can be imagined. Described below are certain specificembodiments. However, these filtration systems are exemplary and shouldnot be construed as restricting the scope of the invention.

[0086] Precoat Filtration Systems Including Microbiological InterceptionEnhanced Nanofiber

[0087] One filtration system of the present invention that utilizesnanofibers treated with the microbiological interception enhancingagent, is an industrial, commercial or municipal filter that uses aprecoat applied to a porous septa. This coating is produced bydispersing particles such as diatomaceous earth, perlite or fibers as aprecoat applied to the porous septa for filtering liquids such as beer,wine, juices, and other liquids used in the food service orpharmaceutical industry. As the liquid contacts the filter cake,unwanted contaminants are removed while also clarifying the liquid. Thecharged nanofibers not only remove negatively charged contaminants inthe liquid much smaller than the pores of the precoat but greatlyimprove the mechanical interception of all particles. The nanofibers maybe used in conjunction with traditional precoat ingredients such asdiatomaceous earth. Only a small amount of nanofibers are needed in theprecoat, generally about 1.5% to about 10% by weight, to produce asignificant effect. Preferably, a hydrophilic microbiologicalinterception enhanced filter medium is used in these applications.

[0088] Filtration Systems Involving Multiple Layers of Filter Medium

[0089] A microbiological interception enhanced filter medium of thepresent invention can include configurations having more than one layerof the microbiological interception enhanced filter medium. A firstmicrobiological interception enhanced filter medium layer may bepositively charged while a second layer may be negatively charged. Thenegatively charged material can be produced by contacting the nanofiberspulp with a negatively charged compound or material such as apolycarboxylic acid mixed with a small quantity of a crosslinking agentsuch as a glycerine. Heating the nanofibers after soaking in such amixture results in the formation of a coating on the nanofibers ofnegatively charged carboxylic acid polymer crosslinked by the glycerine.The multi-layer microbiological interception enhanced filtration systemis capable of intercepting both positively and negatively chargedmicrobiological targets. Again, in applications where NOM is present, anadsorbent prefilter may be needed to preserve the charge on themicrobiological interception enhanced filter medium.

[0090] Filtration Systems with an Adsorbent Prefilter Combined with theMicrobiological Interception Enhanced Filter Medium

[0091] A microporous filter medium of the present invention treated withthe microbiological interception enhancing agent may be used as a flatsheet medium, a pleated medium, or as a spiral wound medium dependingupon the application and the filter housing design. It may be used forjust about any type of fluid filtration including water and air.

[0092] However, the microbiological interception enhanced filter mediummay be less effective in the presence of moderate to high levels of NOMsuch as polyanionic humic acid and fulvic acid, due to the decrease andeventual loss of positive charge on the filter medium in the presence ofsuch acids. Therefore, such applications utilizing the microbiologicalinterception enhanced filter medium alone should be substantially freeof or have low levels of polyanionic acids.

[0093] In filtration systems containing the microbiological interceptionenhanced filter medium that may come in contact with fluids that containNOM, it is prudent to use an adsorbent prefilter to remove the NOM inthe influent prior to it contacting the microbiological interceptionenhanced filter medium. Alternatively, the positively charged filtermedium can be formed into a multitude of layers either as a stack ofsheets or by conversion into a structure. Under this type ofarrangement, the outer layers of the filter medium can be sacrificed toremove the NOM, while the inner layers are protected and providelong-term reduction of microbiological contaminants. Additives thatadsorb or absorb NOM may be incorporated into the microporous structure,including anion exchange resins. To avoid this costly loss ofsacrificial material, the following examples describe other alternativemethods for arranging the protection of the filter medium from theeffects of NOM.

[0094] 1. A Flat Adsorbent Filter Medium as a Prefilter

[0095] The microbiological interception enhanced filter medium may beused in conjunction with adsorbent filtration media that serve tointercept NOM interferences prior to their contact with the chargedmicrobiological interception enhanced filter medium. The microbiologicalinterception enhanced filter medium and one or more layers of anadsorbent filtration medium may be used as a flat sheet composite,spiral wound together, or pleated together. Such an adsorbent filtrationmedium may be manufactured according to U.S. Pat. Nos. 5,792,513 and6,077,588, as well as other processes in the prior art. A particularlysuitable flat sheet adsorbent filtration medium is commerciallyavailable as PLEKX® from KX Industries, L. P., Orange, Conn. The flatsheet filtration medium may contain hydrophilic or hydrophobic particlesthat can also be treated with the microbiological interception enhancingagent, although not necessary, and immobilized on a substrate to provideadded microbiological interception capabilities in addition to thatprovided by the microbiological interception enhanced filter medium. Atleast one adsorbent layer is preferably placed upstream from themicrobiological interception enhanced filter medium to reduce thedeleterious effects of NOM on the microbiological interception enhancedfilter medium. The microbiological interception enhanced filter mediumcan serve as one of the substrates used to support the adsorbent used tofilter NOM from the influent fluid. For example, the upper layer of thePLEKX® structure can be a particulate prefilter. The core of the PLEKX®composite can be primarily composed of an adsorbent with a high affinityfor NOM, and the lower, downstream layer can be the microbiologicalinterception enhanced filter medium. The layers can be bonded into asingle cohesive composite structure using the PLEKX® process describedin the above-mentioned patents. The result is a hgh dirt capacity filterstructure that provides chemical, particulate, and microbiologicalinterception in a single material. The core of the PLEKX® structure caninclude a wide range of ingredients useful for the adsorption ofchemical contaminants.

[0096] 2. GAC Filter Medium as an Adsorbent Prefilter

[0097] The microbiological interception enhanced filter medium may alsobe used in conjunction with a bed of granular adsorbent such as, forexample, a granular activated carbon (GAC) bed. The granular bed filtershould be placed upstream from the microbiological interception enhancedfilter medium to remove any charge-reducing contaminants, such as NOM,from the influent prior to contacting the charged microporous filtermedium.

[0098] 3. Solid Composite Block Filter Medium as an Adsorbent Prefilter

[0099] The microbiological interception enhanced filter medium may alsobe used in conjunction with a solid composite block filter medium,preferably comprising activated carbon, placed upstream from themicrobiological interception enhanced filter medium to remove anycharge-reducing contaminants, such as NOM, from the influent prior tocontact with the microbiological interception enhanced filter medium.The activated carbon block may include, but is not limited to, suchmaterials as activated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, andcombinations thereof to provide additional reduction of contaminantssuch as heavy metals, arsenic, chlorine, and to improve taste and odor.These materials, as well as the activated carbon, may be treated withthe microbiological interception enhancing agent prior to beingconverted into a solid composite by extrusion, compression molding orother processes known to one of skill in the art. Exemplary processesare described in U.S. Pat. Nos. 5,019,311, and 5,189,092. The solidcomposite block can contain an anion-exchange resin that is specificallyselected for its high capacity to adsorb NOM.

[0100] Complete Filtration Devices Combining Adsorbent Prefilters andMicrobiological Interception Enhanced Filter Medim

[0101] One particular embodiment of a filtration system of the presentinvention includes a composite filter medium, as described above,including the microbiological interception enhanced filter medium andthe adsorbent filtration medium. This device is designated to operate asa gravity flow device with a driving pressure of only a few inches watercolumn to a maximum of a few feet of water column. The composite filtermedium is forced to first pass through the adsorbent prefilter and thenthe microbiological interception layer. As shown in FIG. 1, an exemplaryfilter design incorporates the composite filter medium of the presentinvention in a filter housing 10 having a clam shell type enclosure.Filter housing 10 has a top portion 12 having an inlet 14, and a bottomportion 16 having an outlet 18. Residing within a sealed cavity definedby the top portion and bottom portion is the composite filter medium 20shown more accurately in the cross sectional view of FIG. 2. Top portion12 and bottom portion 16 may be formed from a single sheet of apolymeric material and folded over to provide a clam shellconfiguration.

[0102] To assemble the filter, composite filter medium 20 is cut intosubstantially the size and shape of the clam shell enclosure. Compositefilter medium 20 is secured into bottom portion 16 and top portion 12 isplaced over bottom portion 16 and compressed together. The top andbottom shell portions 12, 16 may be welded together creating a weldment22 around the entire periphery of filter medium 20. As illustrated inFIG. 2, there is shown a substantially impermeable interface between thetop and bottom portions and the composite filter medium in the regiondirectly adjacent weldment 22. Excess material on the clam shellenclosure and composite filter medium is simply cut off. It will beunderstood that other methods of sealing the filter medium within thefilter housing may be used such as, but not limited to, adhesives,mechanical clamps, and the like. Although the filter design has a clamshell enclosure, the filter design is not limited to such. Any enclosurethat may be sealed such that an influent will not bypass the filtermedium would be suitable.

[0103] In referring back to FIG. 2, the seal formed between compositefilter medium 20 and top portion 12 and bottom portion 16 is such thatwater being filtered is forced to follow the path illustrated by arrowsA and B, and cannot bypass composite filter medium 20. In fact, at theperiphery of composite filter medium 20, the pressure exerted by theseal increases the density of the filter medium so that contact time ofthe water being filtered with composite filter medium 20 in thisperipheral region is increased and filtration efficiency enhanced.

[0104] During production of the filter, assurances concerning the sealand assembly integrity may be obtained using a vision system, and gas oraerosol pulse testing. The gas or aerosol pulse test uses a tiny pulseof dilute butane or fog-oil smoke that is entirely adsorbed orintercepted by an intact filter, but will significantly penetrate adefective filter. Other off-line test procedures known to one of skillin the art may be used to methodically examine the quality of the sealbetween the filter medium and the enclosure.

[0105] The wall of the filter housing may be sufficiently thin andflexible so that when the filter is contacted with water, the modestpressure produced by the hydrostatic load of the incoming water causestop portion 12 and bottom portion 16 to bow away slightly from andprovide a clearance space between the inner surface of top portion 12and bottom portion 16, and composite filter medium 20. This clearancespace assists in distributing the water across the influent surface ofcomposite filter medium 20 and provides drainage of the effluent intooutlet 18.

[0106] Referring to FIG. 3, there is shown a front plan view of afiltration system 30 of the present invention useful in providingpotable water in a gravity flow device that may be useful in developingcountries where safe, potable water of suitable microbiological qualityis scarce. Although water is discussed as the liquid influent, it iswithin the scope of the invention to contemplate the filtration of otherliquids. Filtration system 30 has a first reservoir 35 that is a rawwater collection transport container. First reservoir 35 may be a bagconfiguration as shown constructed of a substantially leak proofmaterial such as a polymeric material, i.e., polyester, nylon, apolyolefin such as polyethylene, polyvinyl chloride, and multi-layerfilms of the like. For ease of use, first reservoir 35 may have areinforced opening and a handle 36 for carrying and hanging firstreservoir 35 to provide a pressure head during filtration. Preferably,first reservoir 35 has a resealable opening 37 that when closed providesa substantially water-tight seal. Such resealable openings are known toone of skill in the art or may include a threaded opening with ascrew-on cap.

[0107] First reservoir 35 is preferably equipped with an output hose 40such that water stored in the reservoir may be drained for filtrationand eventual use. Output hose 40 is preferably made with a food-safegrade of flexible polymer. Output hose 40 may be opened and closed usinga simple clamp. Output hose 40 may be permanently attached to firstreservoir 35 by ultrasonic welding or retained simply by friction.Output hose 40 preferably has an internal extension end 42 within firstreservoir 35 such that internal extension end 42 extends above thebottom of the first reservoir 35 to provide an area for capturingsediment that can settle prior to water filtration. By limiting theamount of sediment present in the influent prior to water filtration,the useful life of the filtration system is prolonged.

[0108] Output hose 40 connects first reservoir 35 to a filter 10,described above, including the composite filter medium of the presentinvention. A clamp 45 may be fitted on output hose 40 at any point alongthe length of output hose 40. Such clamps are well known in the art andmay be a simple one piece configuration made of a flexible polymer ormetal. When the clamp is in an open position, water from first reservoir35 flows freely into filter 10. Filter 10 is removably connected tooutput hose 40. The outlet of filter 10 is then connected to a secondreservoir 50. Second reservoir 50 serves as a collection vessel for thefiltered water or effluent. Alternatively, filter 10 and secondreservoir 50 may be connected together via a second output hose (notshown). Second reservoir 50 generally is equipped with a means fordispensing the filtered water.

[0109] The above filtration system may be used as follows. A user takesfirst reservoir 35, with or without output hose 40 attached thereto, toa water source. If output hose 40 is still attached to first reservoir35, clamp 45 must be in a closed position or first reservoir 35 must besealed by other means. First reservoir 35 is filled with a quantity ofraw water and its opening again sealed while the user carries firstreservoir 35 back to a preferred location such as a residence. It ispossible that the raw water is contaminated with microorganisms andchemical contaminants and may not be potable. To facilitate filtration,first reservoir 35 is suspended or hung from a support means. Dependingupon any significant sediment present as evidenced by turbidity, the rawwater is allowed to remain suspended for a period of time sufficient forthe sediment to settle below the height of internal extension end 42 ofoutput hose 40 within first reservoir 35. Of course, should the water berelatively clear, there is no need to suspend first reservoir 35 forsuch a period of time. Output hose 40 is attached to first reservoir 35,if previously detached, and secured to filter 10. Filter 10 is securedto second reservoir 50 for collecting the filtered water. Clamp 45 isthen placed in an open position and the water is allowed to flow intofilter 10 wherein the water once treated through composite filter medium20, is rendered potable, and collected in second reservoir 50. Topreserve the potability of the filtered water, the surfaces of secondreservoir 50 may be made from or treated with a disinfectant or with themicrobiological interception enhancing agent. Preferably, thedisinfectant used would not alter or affect the taste of the water.

[0110] Typical water flow rates are about 25 to about 100 ml/minute fora device equipped with a filter of about 3″×5″ size and operated atabout 6″ water column pressure. This provides one liter of potable waterin about 10 to 40 minutes having at least about 6 log reduction inbacteria and at least about 4 log reduction in viral contaminants.Continual use of filter 10 will likely develop, by progressivedeposition thereon, a layer of particles that will slow the flow rateuntil the filtration process takes an unacceptable amount of time.Although the flow rate is diminished, the filter will maintain itsmicrobiological interception capabilities for an extended period.

[0111] Another gravity flow device incorporating a filter medium of thepresent invention includes an exemplary carafe design as illustrated inFIG. 4 for filtering, storing and dispensing filtered water or otherfluids. Although the carafe shown is primarily round, the carafe 60 mayassume any shape depending upon its use and environment, and is a matterof design choice. A basic carafe has a housing 62 with a handle 64 andcover 66. Carafe 60 is divided into a lower reservoir or storage chamber68 and an upper reservoir 78 that are enclosed by lid 70 and cover 66located within housing 62. Spout 72 facilitates the removal of filteredwater through outlet 74 of storage chamber 68.

[0112] Upper reservoir 78 and storage chamber 68 are separated bypartition 80 that is provided with a filter receiving receptacle 85having an opening (not shown) in the bottom thereof. In one embodiment,a flat composite filter medium 76 of the present invention is placedinto filter receiving receptacle 85 with a water tight seal to segregateupper reservoir 78 and storage chamber 68. Placement of filter medium 76into filter receptacle 85 may be accomplished using means known to oneof skill in the art including, but not limited to, a snap or hingedmechanism. Filter medium 76 is preferably manufactured as a replaceablecartridge. Other features of the carafe design may be incorporated intothe present invention without departing from the scope of the invention.The filter medium may comprise any microporous structure having a meanflow path of less than about 1 micron and so treated as to provide atleast about 4 log reduction of microbiological contaminants smaller thanthe mean flow path of the filter medium. Preferably, the filter mediumhas a volume of less than about 500 cm³ and has an initial flow rate ofgreater than about 25 ml/minute.

[0113] A user would pour raw water into upper reservoir 78 and allow theraw water to pass through filter medium 76 under the influence ofgravity. Filtered water is collected in storage chamber 68. As the rawwater passes through the filter medium of the present invention withsufficient contact time, the filter medium renders the water potable byproviding a high titer reduction of microorganisms. The log reductionvalue (LRV) of microorganisms is dependent upon the contact time of thefilter medium with the flowing water. To provide about 8 log reductionvalue of microorganisms, the required contact time is about 6 to about10 seconds.

[0114] Carafe 60 may also have an indicator (not shown) that allows auser to keep track of the age of the filter to gauge when the usefullife of the filter medium has been expended. Other types of indicatorsmay also be used such as an indicator for indicating the number ofrefills of carafe 60, for measuring the volume of water or liquid thatpasses through the filter medium, and the like.

[0115] Other Filtration Systems

[0116] A filter medium of the present invention, in particular, thecomposite filter medium, may also be incorporated into a point-of-useapplication such as a sports bottle design for use as a personal waterfiltration system operating under a slight pressure, about 1 psi. Asuitable sports bottle design is disclosed in International PatentApplication No. WO 01/23306 wherein the filter medium may beincorporated into the filter receptacle of the sports bottle.

[0117] For other point-of-use applications, the microbiologicalinterception enhanced filter medium of the present invention may furtherbe incorporated into end-of-tap (EOT), under-sink, counter-top, or othercommon consumer or industrial filtration systems and configurations foruse in pressurized systems. The filter system may include a prefiltercomprising a bed of adsorbent particles or a solid adsorbent compositeblock. The microbiological interception enhanced filter medium can be apleated or a spiral wound construction, or formed into a thick mat byvacuum formation on a suitable mandrel to create a wet-formed ordry-formed cartridge.

EXAMPLES

[0118] The following examples are provided to illustrate the presentinvention and should not be construed as limiting the scope of theinvention.

[0119] Porometry studies were performed with an Automated Capillary FlowPorometer available from Porous Materials, Inc., Ithaca, N.Y. Parametersdetermined, using standard procedures published by the equipmentmanufacturer, include mean flow pore size and gas (air) permeability.The flow of air was assayed at variable pressure on both the dry and wetfilter medium. Prior to wet runs, the filter medium was initiallyimmersed in silicon oil for at least 10 minutes while held under highvacuum.

[0120] Zeta or streaming potential of various filter media wasdetermined using streaming potential and streaming current measured witha BI-EKA Electro-Kinetic Analyzer available from Brookhaven Instruments,of Holtsville, N.Y. This instrument includes an analyzer, a flat-sheetmeasuring cell, electrodes, and a data control system. The analyzerincludes a pump to produce the pressure required to pass an electrolytesolution, generally 0.0015M potassium chloride, from a reservoir,through the measuring cell containing a sample of the filter mediumdescribed herein. Sensors for measuring temperature, pressure drop,conductivity and pH are disposed externally of the cell. In accordancewith this method the electrolyte solution is pumped through the porousmaterial. As the electrolyte solution passes through the sample, adisplacement of charge occurs. The resulting “streaming potential and/orstreaming current” can be detected by means of the electrodes, placed ateach end of the sample. The zeta (streaming) potential of the sample isthen determined by a calculation according to the method of Fairbrotherand Mastin that takes into account the conductivity of the electrolyte.

[0121] Bacterial challenges of the filter media were performed usingsuspensions of Escherichia coli of the American Type Culture Collection(ATCC) No. 11775 to evaluate the response to a bacterial challenge. Theresponse to viral challenges was evaluated using MS-2 bacteriophage ATTCNo. 15597-B1. The Standard Operating Procedures of the ATCC were usedfor propagation of the bacterium and bacteriophage, and standardmicrobiological procedures, as well known in the art, were used forpreparing and quantifying the microorganisms in both the influent andeffluent of filters challenged with suspensions of the microbiologicalparticles.

Examples 1-3

[0122] Filter Medium Made with Untreated Lyocell Fibers (Comparative)

[0123] Filter medium made from untreated lyocell fibers having amean-flow path of about 0.3 to about 0.6 microns were prepared inaccordance with the following method.

[0124] Dry EST-8 binder fibers having a weight of 0.45 g, commerciallyavailable from MiniFibers, Inc., was fully dispersed in 1.0 L ofdeionized water in a kitchen style blender on a pulse setting.Fibrillated lyocell fibers with a Canadian Standard Freeness of 45 andhaving a dry weight of 120.0 g were added as wet pulp to the dispersedbinder fibers. The dispersed fiber mixture was blended for another 15seconds. The fiber mixture was poured into a larger industrial Waringblender with an additional 1.0 L of deionized water and blended for anadditional 15 to 30 seconds. The fiber mixture was poured into a30.5×30.5 cm² stainless steel FORMAX® paper deckle filled with about12.0 L of deionized water and fitted with a 100 mesh forming screen. A30×30 cm² stainless steel agitator plate having 60 holes of 2 cm indiameter was used to plunge the fiber mixture up and down from top tobottom about 8 to 10 times. The water was removed from the fiber mixtureby pulling a slight vacuum below the deckle to cause the fibers to formon the wire. Once the bulk of the water is removed, supplementaldewatering is accomplished with a vacuum pump to remove additionalexcess moisture and to create a relatively smooth, flat, fairly thinpaper-like sheet. The resulting sheet is separated from the screen andcombined with a blotter sheet on both top and bottom. The combination ofsheets is gently rolled with a 2.27 kg marble rolling pin to removeexcess water and smooth out the top surface of the sheet. The sheet isthen placed between two fresh and dry blotter sheets and placed on aFORMAX® sheet dryer for about 10 to about 15 minutes at about 120° C.The dried filter medium is separated from the blotter sheets anddirectly heated on the FORMAX® sheet dryer for about 5 minutes on eachside to activate the dry binder fibers.

[0125] Table I shows the porometry and air permeability test resultsperformed on filter medium made from untreated lyocell fibers of varyingthicknesses made using the above process. TABLE I Mean Flow Path andPorometry of Filter Medium Made With Untreated Lyocell Fibers SampleThickness Mean Flow Path Gas Permeability Example # (mm) (μm) (L/cm² at1 psi) 1 0.45 0.3804 5.48 2 0.66 0.6708 4.50 3 0.63 0.4316 5.30

[0126] The resulting filter medium made with untreated lyocell fibershad a reproducible streaming potential of about −9.0 millivolts.

Example 4

[0127] Filter Medium Made with Lyocell Fibers Treated with theMicrobiological Interception Enhancing Agent

[0128] To a blender were added 12.0 g dry weight lyocell fibers as a 10%by weight wet pulp having a Canadian Standard Freeness of about 45, 0.45g SHORT STUFF® EST-8 binder fibers, and 1.0 L deionized water. Themixture was blended until the fibers were fully dispersed. To theblender was added 3.0 ml of MERQUAT® 100 as a 30% aqueous solution andthe fibers blended with the MERQUAT® 100 for about 10 seconds and leftto stand for at least about 6 hours. After about 6 hours, the fiberswere poured into a standard 8 inch Brit jar fitted with a 100 meshforming wire and excess water removed under vacuum. The resulting pulpsheet was rinsed with 500 ml of deionized water. The excess water wasagain removed by vacuum.

[0129] A dilute silver nitrate solution was poured uniformly over thepulp sheet to provide full exposure and saturation, providing about0.1425 g of silver per sheet. The silver nitrate solution was left onthe pulp sheet for at least about 15 minutes and excess water removedunder vacuum pressure. The silver-treated pulp sheet was then torn intosmall pieces and placed in a WARING® blender and re-dispersed in 2.0 Lof deionized water. A second 3.0 ml portion of the MERQUAT® 100 solutionwas added to the dispersion and the mixture blended for about 10 minutesand the contents poured into a 30.5×30.5 cm² stainless steel FORMAX®paper deckle fitted with a 100 mesh forming screen. Paper-like sheets ofthe microbiological interception enhanced filter medium were made in thesame manner as the untreated lyocell filter media described in Examples1 to 3.

[0130] The zeta potential of the filter medium was consistently greaterthan about +10 millivolts at a pH of about 7.0.

Examples 5-23

[0131] Comparison of Microbiological Interception with theMicrobiological Interception Enhanced Filter Medium of the PresentInvention and the Untreated Lyocell Filter Medium

[0132] Sheets of fibrillated lyocell filter medium either untreated ortreated with MERQUAT® 100 and silver, as described in Examples 1 to 4,were folded twice and cut into standard cone-shaped funnels and placedinto small sterilized glass funnels. Deionized water was used to pre-weteach filter medium. Approximately 125 ml of various microbiologicalchallenges were poured through the filters and the effluents collectedin sterile 250 ml Erlenmeyer flasks. The effluents were subjected toserial dilution in duplicate and plated on petri dishes followingstandard laboratory procedures as required for each organism and leftovernight in 37° C. heated incubators. The next day all test resultswere recorded. Table II summarizes the log reduction values of a seriesof tests run using microbiological challenges made with de-ionizedwater. TABLE II LRVs of Filter Media Made With Treated And UntreatedFibrillated Lyocell Fibers E. coli LRV E. coli LRV MS2 LRV MS2 LRV Ex #(Treated) (Untreated) Ex # (Treated) (Untreated) 5 9.2 — 14 7.47 — 6 9.2— 15 7.47 — 7 9.2 — 16 7.47 — 8 9.2 — 17 7.76 — 9 9.2 — 18 7.76 — 10 9.2— 19 7.76 — 11 9.4 <1.0 20 8.58 <1.0 12 7.65 <1.0 21 8.58 <1.0 13 9.98<1.0 22 8.67 <1.0 23 8.19 <1.0

[0133] As illustrated in Table II, the filter medium made from lyocellfibers with MERQUAT® 100 and silver provided significant microbiologicalinterception capabilities as compared to filter medium made fromuntreated lyocell fibers. The efficacy of the microbiologicalinterception enhanced filter medium when challenged with MS2 viralparticles illustrates that a filtration system of the present inventionwould prove effective in removing nano-sized pathogens such as viruses.

Examples 24-27

[0134] Microbiological Interception Capability of the Filter Medium Madewith Treated Lyocell Fibers in the Presence of Polyanionic Acids

[0135] As discussed above, NOM such as polyanionic acids reduce thepositive zeta potential and, thereby, reduce the efficacy of themicrobiological interception enhanced filter medium. After exposure to500 ml humic acid (0.005 g/1.0 L H₂O), the zeta potential of themicrobiological interception enhanced filter medium decreased from +14.1to −14.4. Likewise, after exposure to 500 ml fulvic acid (0.005 g/1.0 LH₂O), the zeta potential of the microbiological interception enhancedfilter medium decreased from +10.1 to −8.9. Examples 24 to 27 show thereduction in microbiological interception capabilities of the filtermedium made with lyocell fibers treated with MERQUAT® 100 and silver inthe presence of humic and fulvic acid solutions.

[0136] Small discs of the filter medium treated with MERQUAT® 100 andsilver were folded and placed in small sterilized glass funnels to forma filter and pre-wetted with de-ionized water. Challenge solutions of E.coli and MS2 viral particles were made with humic acid and fulvic acid,respectively. Approximately 125 ml of the challenge solutions werepoured through the filters and the effluent collected in sterile 250 mlErlenmeyer flasks. The effluent was diluted and plated on petri dishesfollowing standard laboratory procedures. Log reduction values of E.coli and MS2 viral particles are summarized in Tables IIII and IV below.TABLE III LRVs Of The Microbiological Interception Enhanced Filter MediaIn The Presence Of Fulvic Acid Ex # E. coli (LRV) MS2 (MRV) 24 4.68 4.23

[0137] TABLE IV LRVs Of The Microbiological Interception Enhanced FilterMedia In The Presence Of Humic Acid Ex # E. coli (LRV) MS2 (MRV) 25 3.784.23 26 3.02 1.64 27 6.73 3.58

[0138] Clearly, the LRVs of the microbiological interception enhancedfilter media in the presence of NOM are significantly lower than the 7to 9 log reduction of E. coli and MS2 absent NOM interference as shownin Table II.

Examples 28-46

[0139] Microbiological Interception Capability of the Filter Medium Madewith Treated Lyocell Fibers and an Adsorbent Layer in the Presence ofPolyanionic Acids

[0140] In order to decrease the impact of NOM on the filter medium asshown in Examples 24 to 27, an adsorbent prefilter was added to thefilter to remove or trap the NOM in the influent prior to contact withthe filter medium. The adsorbent layer is PLEKX® made with 600 g/m² offinely ground coal-based activated carbon having a surface area of 1000m²/g, and is commercially available from KX Industries, L. P.

[0141] A composite filter medium combining two (2) layers of a filtermedium made with the microbiological interception enhanced filter mediumand one (1) PLEKX® layer was fitted in ceramic Buchner funnels over ametal drainage screen. The three (3) layers were secured in each Buchnerfunnels with a hot melt adhesive to prevent any bypass of the influent.A head pressure of water about 5 cm in depth was maintained in theBuchner funnel at all times. The filters of examples 28 to 34 werecharged with sterile deionized water prior to the microbiologicalchallenge and were not exposed to either humic or fulvic acids. Resultsshown in Table V below show that the efficacy of the composite filtermedium with the addition of the adsorbent layer is similar to theresults shown in Table II above.

[0142] The filters of examples 35 to 40 were charged with 500 ml of ahumic acid solution (0.005 g/l L H₂O) prior to the microbiologicalchallenge. Results are shown in Table VI below. The filters of examples41 to 46 were charged with 500 ml of a fulvic acid solution (0.005 g/1 LH₂O) prior to the microbiological challenge. Results are shown in TableVII below. TABLE V LRVs Of Filter Media Made With Fibrillated LyocellFibers Treated With MERQUAT ® 100 And Silver With PLEKX ® Absent NOMInterference Ex # E. coli LRV Ex # MS2 LRV 28 7.89 31 8.06 29 7.89 328.06 30 7.89 33 8.49 34 8.49

[0143] TABLE VI LRVs Of Filter Media Made With Fibrillated LyocellFibers Untreated And Treated With MERQUAT ® 100 And Silver With PLEKX ®In The Presence Of Humic Acid Ex # E. coli LRV Ex # MS2 LRV 35 8.75 388.53 36 8.75 39 8.53 37 8.75 40 8.53

[0144] TABLE VII LRVs Of Filter Media Made With Fibrillated LyocellFibers Untreated And Treated With MERQUAT ® 100 And Silver With PLEKX ®In The Presence Of Fulvic Acid Ex # E. coli LRV Ex # MS2 LRV 41 8.85 447.77 42 8.85 45 7.77 43 8.85 46 7.77

[0145] The data shows that the use of an adsorbent prefilter such asPLEKX®, placed upstream from the microbiological interception enhancedfilter medium, maintained or improved the microbiological interceptioncapabilities of the filter medium by removing the NOM in the influentbefore the influent contacted the microbiological interception enhancedfilter medium. The adsorbent prefilter medium does not need to betreated with the microbiological interception enhancing agent tomaintain the efficacy of the microbiological interception enhancedfilter medium. It may be a cost saving measure not to treat theadsorbent prefilter medium. Thus, a composite filter medium includingthe microbiological interception enhanced filter medium and an adsorbentlayer positioned upstream from the microbiological interception enhancedfilter medium would be robust enough to withstand interference from NOM.

Examples 47-48

[0146]E. coli Challenges of a Filtration System of the Present Invention

[0147] Two filtration systems of the present invention, as shown in FIG.3, including a composite filter medium comprising two (2) layers of anadsorbent filter medium, PLEKX® made with 600 g/m² of coal-basedactivated carbon having a surface area of 1000 m²/g, and a single layerof the microbiological interception enhanced filter medium made fromtreated fibrillated lyocell fibers as described in Example 4 wereassembled using the clam shell filter design of FIGS. 1 and 2 describedabove. A supporting layer of PLEKX® was placed in the bottom of eachfilter housing and glued into place using an ethylene-vinyl acetate(EVA) hot melt. The layer of microbiological interception enhancedfilter medium was glued to the first PLEKX® layer, followed by a secondPLEKX® layer that was also glued into place atop the microbiologicalinterception enhanced filter medium. This configuration uses only one ofthe PLEKX® layers as an adsorbent prefilter, while the other PLEKX®layer serves primarily as a support for the microbiological interceptionenhanced filter medium. The outside edges of the housing were also gluedand pressed firmly together to prevent any bypass leakage to the outsideof the housing. The dimensions of active filter area within the boundarydefined by the hot melt material was between 5 cm to 6 cm wide and 8 cmto 10 cm long, providing an active filter area of between 40 cm² and 60cm². While hot melt was used during this prototype testing, filterassembly using ultrasonic or other welding methods may be applied duringcommercial production.

[0148] A 0.635 cm (0.25 inch) inside diameter hose was attached to theinlet of the filter housing using a plastic fitting and glued securelyinto place. The outlet of the filter was open to allow fluid to exit thefilter housing. The hose attached to the filter inlet was attached to aglass Pyrex funnel to produce a total inlet water column ofapproximately 30 cm to 60 cm. Test suspensions were poured into thefunnel to challenge the filter with various organisms.

[0149] Approximately 500 ml of de-ionized water was poured through thefiltration system to pre-wet the filter medium inside the housing. ForE. coli testing, a hose and funnel with a combined height of 60 cm wasused to provide head pressure. The flow rate at this influent pressurewas 70 ml/min. A challenge suspension of E. coli was poured through thesystem and the effluents collected in sterile 250 ml Erlenmeyer flasks.The effluents were subjected to serial dilution in duplicate and platedon petri dishes following standard laboratory procedures and leftovernight in 37° C. heated incubators. The next day all test resultswere recorded and these are listed in Table VIII below. TABLE VIIIMicrobiological Challenges Of A Filtration System Of The PresentInvention With E. coli # of colonies Ex # No. of E. coli in Challengeforming/plate LRV 47 8.4 × 10⁸ 0 8.92 48 8.4 × 10⁸ 0 8.92

[0150] Thus, a filtration system of the present invention utilizing acomposite filter medium including a PLEKX® prefilter and themicrobiological interception enhanced filter medium will provide greaterthan 8.5 log reduction of E. coli at a flow rate of approximately 1 to 2ml/minute·cm².

Example 49-51

[0151] MS2 Challenges of a Filtration System of the Present Invention

[0152] Three filters were constructed in a similar fashion as for the E.coli challenge as described in examples 47 and 48 above, for determiningthe viral interception capability of a filtration system of the presentinvention. In two filters, Examples 49 and 50, a layer of netting wasinstalled at the bottom, effluent side, of the filter housing, followedby a layer of the microbiological interception enhanced filter medium,followed by a single top layer of PLEKX® made with 600 g/m² ofcoal-based activated carbon having a surface area of 1000 m²/g. For thethird filter, Example 51, the plastic netting was replaced with a metal100 mesh screen as the bottom support layer. For the MS2 challenge, ahose and funnel of 30 cm was used to reduce the flow rate and allow forlonger contact time through the composite filter medium. De-ionizedwater was poured through the system to pre-wet the layers and verifythat the housing had no leaks. A flow rate of 38 ml/minute was recordedfor the 30 cm high water column. After the de-ionized water exitedthrough the system, the MS2 challenge solution was poured through thesystem. The effluent was collected in sterile Erlenmeyer flasks, dilutedand plated on Petri dishes following standard procedures for MS2 andleft overnight. The next day all test results were recorded and listedin Table IX below. TABLE IX Microbiological Challenges Of The FilterWith MS2 Bacteriophage # of colonies Ex # No. of MS2 in Challengeforming/plate LRV 49 6.12 × 10⁸ 0 8.78 50 6.12 × 10⁸ 0 8.78 51 6.12 ×10⁸ 0 8.78

[0153] A filtration system of the present invention utilizing acomposite filter medium including a PLEKX® prefilter and themicrobiological interception enhanced filter medium is shown to providegreater than 8.5 log reduction of MS2 at a flow rate of approximately0.75 ml/minute-cm².

Examples 52 and 53

[0154] Long Term MS2 Challenges of a Filtration System of the PresentInvention

[0155] These examples assess the effectiveness of a filtration system ofthe present invention when challenged with MS2 bacteriphage and having acomposite filter medium including two (2) layers of the microbiologicalinterception enhanced filter medium and two (2) layers of PLEKX® asdescribed earlier.

[0156] Two filtration systems of the present invention were prepared bysecuring a 100 mesh screen inside a filter enclosure as shown in FIGS. 1and 2. Two layers of the microbiological interception enhanced filtermedium were placed atop the mesh screen followed by two layers ofPLEKX®. Each layer was glued securely in place to prevent bypass. Thefilter enclosure was sealed with the glue as well. A 0.635 cm (0.25inch) inner diameter hose was attached securely to the inlet of thefilter housing. The outlet of the filter housing was open to allow thepassage of fluid. A funnel was securely attached to each filter toprovide one with a 25.4 cm (10 inches) water column, and the otherfilter with a 10.2 cm (4 inches) water column for testing ofmicrobiological challenges.

[0157] Deionized water, approximately 500 ml, was passed through eachfiltration system to pre-wet the filter medium and verify that no bypasswas occurring. Subsequently 500 ml of an MS2 challenge, prepared indeionized water, was passed through each system. The effluents werecollected in sterile Erlenmeyer flasks, diluted and plated on Petridishes following standard procedures for the organism and leftovernight. After 24 hours, an additional 500 ml of deionized water waspassed through the system followed by another 500 ml MS2 challenge. Thisprotocol was continued every 24 hours until the filter media no longerprovided an LRV above 4. The results are shown in Tables X and XI below.TABLE X Example 52: Efficacy Of A Filtration System Of The PresentInvention With A 25.4 cm Water Column Total Amount Time in Use No. ofMS2 in Flow Rate of H₂O (L) (hours) Challenge LRV (ml/min.) 1.0 0 2.84 ×10⁸ 8.45 28 2.0 24 4.93 × 10⁸ 7.97 32 3.0 48 4.57 × 10⁸ 8.66 32 4.0 724.55 × 10⁸ 7.52 36 5.0 96 1.76 × 10⁹ 5.65 38 6.0 120 1.39 × 10⁹ 5.66 387.0 144 1.48 × 10⁹ 3.03 36 8.0 168 1.56 × 10⁹ 2.22 30

[0158] TABLE XI Example 53: Efficacy Of A Filtration System Of ThePresent Invention With A 10.2 cm Water Column Total Amount Time in UseNo. of MS2 in Flow Rate of H₂O (L) (hours) Challenge LRV (ml/min.) 1.0 02.05 × 10⁹ 9.31 12 2.0 24 2.16 × 10⁹ 9.33 15 3.0 48 1.46 × 10⁹ 9.16 154.0 72 1.05 × 10⁹ 9.02 17 5.0 96 1.52 × 10⁹ 9.18 16 6.0 120 1.31 × 10⁹9.12 13 7.0 144 1.19 × 10⁹ 9.08 13 8.0 168 1.32 × 10⁹ 8.23 13 9.0 1928.67 × 10⁸ 8.93 16 10.0 216 1.34 × 10⁹ 9.13 10 11.0 240 1.10 × 10⁹ 9.0411 12.0 264 1.24 × 10⁹ 7.76 9 13.0 288 1.24 × 10⁹ 8.27 9 14.0 316 1.02 ×10⁹ 3.62 7 15.0 340 1.04 × 10⁹ 3.41 8 16.0 364 1.03 × 10⁹ 3.36 10 17.0388 1.07 × 10⁹ 3.03 10

[0159] The useful life of the filtration system of Example 52 with apressure head of 25.4 cm provided an acceptable MS2 log reduction for6.0 L of water for 120 hours. However, when the pressure head was 10.2cm, as in Example 53, the useful life of the filtration systems wasextended, providing acceptable log reduction values of MS2 for a volumeof 13.0 L of water and 364 hours. It is apparent that the flow rate willaffect the microbiological interception capabilities of the filtrationsystem. From the results of Examples 52 and 53, a lower flow rate willprovide more effective microbiological interception due to greatercontact time of the microorganisms with the filter medium.

Example 54

[0160] Long Term E. coli Challenges of a Filtration System of thePresent Invention

[0161] This example assesses the effectiveness of a filtration system ofthe present invention having a composite filter medium including two (2)layers of the microbiological interception enhanced filter medium andtwo (2) layers of PLEKX® as described earlier.

[0162] Deionized water, approximately 500 ml, was passed through thefiltration system to pre-wet the filter medium and verify that no bypasswas occurring. Subsequently, 500 ml of the E. coli challenge, preparedin deionized water, was passed through the filter. The effluent wascollected in a sterile Erlenmeyer flasks, diluted and plated on Petridishes following standard procedures for E. coli and left overnight.After 24 hours, an additional 500 ml of deionized was passed through thesystem followed by another 500 ml E. coli challenge. This protocol wascontinued every 24 hours until the filter medium no longer provided anLRV above 4. The results are shown in Table XII below. TABLE XII Example54: Efficacy Of A Filtration System Of The Present Invention With A 25.4cm Water Column Total Amount Time in Use No. of E. coli Flow Rate of H₂O(L) (hours) in Challenge LRV (ml/min.) 1.0 0 9.33 × 10⁸ 8.99 28 2.0 247.86 × 10⁸ 8.89 32 3.0 48 2.86 × 10⁸ 8.46 27 4.0 72 1.35 × 10⁹ 8.37 215.0 96 1.18 × 10⁹ 8.07 17 6.0 120  8.4 × 10⁸ 7.38 18 7.0 144 1.09 × 10⁹4.95 12 8.0 168  3.6 × 10⁸ 3.50 16 9.0 192 6.13 × 10⁸ 3.61 12

[0163] The filtration system of Example 50 provided acceptableperformance after 6.0 L of water had passed through the system at anaverage flow rate of about 24 ml/minute wherein the head pressure wascaused by a 25.4 cm water column.

[0164] While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

What is claimed is:
 1. A filter medium comprising: a microporousstructure having a mean flow path of less than or equal to about 1micron; and a microbiological interception enhancing agent comprising acationic metal complex capable of imparting a positive charge on atleast a portion of said microporous structure.
 2. The filter medium ofclaim 1 wherein said microporous structure comprises a plurality ofnanofibers having a fiber diameter of less than about 1000 nanometers.3. The filter medium of claim 2 wherein the nanofibers comprise organicfibers, inorganic fibers, or a mixture thereof.
 4. The filter medium ofclaim 2 wherein the nanofibers comprise glass fibers.
 5. The filtermedium of claim 2 wherein the nanofibers comprise polymer fibers.
 6. Thefilter medium of claim 5 wherein at least a portion of the polymerfibers are substantially fibrillated.
 7. The filter medium of claim 5wherein the nanofibers comprise cellulose fibers.
 8. The filter mediumof claim 7 wherein at least a portion of the cellulose fibers aresubstantially fibrillated.
 9. The filter medium of claim 8 wherein thenanofibers comprise substantially fibrillated lyocell fibers.
 10. Thefilter medium of claim 9 wherein at least a portion of the fibrillatedlyocell fibers are about 1 millimeter to about 8 millimeters in lengthand have a diameter of less than or equal to about 1000 nanometers. 11.The filter medium of claim 9 wherein the fibrillated lyocell fibers havea Canadian Standard Freeness of less than or equal to about
 100. 12. Thefilter medium of claim 9 wherein the fibrillated lyocell fibers have aCanadian Standard Freeness of less than or equal to about
 45. 13. Thefilter medium of claim 1 wherein said microporous structure is amembrane comprising an organic material, an inorganic material, or amixture thereof.
 14. The filter medium of claim 13 wherein the membranecomprises a polymer material.
 15. The filter medium of claim 1 whereinsaid microporous structure is combined with an adsorbent prefiltermedium containing activated carbon, activated alumina, zeolites,diatomaceous earth, silicates, aluminosilicates, titanates, bone char,calcium hydroxyapatite, manganese oxides, iron oxides, magnesia,perlite, talc, polymeric particulates, clay, iodated resins, ionexchange resins, ceramics, or combinations thereof.
 16. The filtermedium of claim 1 wherein said microbiological interception enhancingagent consists of a cationic metal complex wherein a cationic materialon a surface of said microporous structure has an associated counter iontherewith and wherein a biologically active metal is caused toprecipitate with at least a portion of the counter ion associated withthe cationic material.
 17. The filter medium of claim 16 wherein thecationic material is adsorbed, chemically bonded or crosslinked to atleast a portion of a surface of said microporous structure.
 18. Thefilter medium of claim 16 wherein the cationic material having a counterion associated therewith is selected from the group consisting ofamines, amides, quaternary ammonium salts, imides, benzalkoniumcompounds, biguanides, aminosilicon compounds, polymers thereof, andcombinations thereof.
 19. The filter medium of claim 16 wherein thecationic metal complex includes a biologically active metal selectedfrom the group consisting of silver, copper, zinc, cadmium, mercury,antimony, gold, aluminum, platinum, palladium, and combinations thereof.20. The filter medium of claim 1 wherein the cationic metal complex isformed by treating at least a portion of said microporous structure witha cationic material comprising a homopolymer of diallyl dimethylammonium halide followed by precipitation of silver with at least aportion of the halide counter ion associated with the homopolymer ofdiallyl dimethyl ammonium halide.
 21. The filter medium of claim 20wherein the homopolymer of diallyl dimethyl ammonium halide has amolecular weight of about 400,000 Daltons.
 22. The filter medium ofclaim 1 further including an adsorbent prefilter adapted to removecharge-reducing contaminants from an influent prior to the influentcontacting said microporous structure.
 23. The filter medium of claim 1wherein said microporous structure incorporates one or more materialsselected from the group consisting of activated carbon, activatedalumina, zeolites, diatomaceous earth, silicates, aluminosilicates,titanates, bone char, calcium hydroxyapatite, manganese oxides, ironoxides, magnesia, perlite, talc, polymeric particulates, clay, iodatedresins, ion exchange resins, ceramics, and combinations thereof.
 24. Thefilter medium of claim 1 wherein said microporous structure furtherincludes a binder.
 25. The filter medium of claim 1 wherein saidmicrobiological interception enhancing agent consists of asilver-amine-halide complex wherein a cationic amine on a surface ofsaid microporous structure has an associated halide counter iontherewith and wherein silver is caused to precipitate with at least aportion of the halide counter ion associated with the cationic amine.26. The filter medium of claim 25 wherein the cationic amine is ahomopolymer of diallyl dimethyl ammonium halide having a molecularweight of greater than or equal to about 400,000 Daltons.
 27. Acomposite filter medium comprising: as adsorbent prefilter havingimmobilized therein a material capable of removing charge-reducingcontaminants; a microporous structure, disposed downstream from saidadsorbent layer, comprising a plurality of nanofibers, said microporousstructure having a mean flow path of less than about 0.6 micron; and amicrobiological interception enhancing agent comprising asilver-cationic material-halide complex having a high charge density,coated on at least a portion of a surface of at least some of theplurality of fibers of said microporous structure.
 28. The filter mediumof claim 27 wherein said adsorbent prefilter is located between aparticulate prefilter and said microporous structure.
 29. The filtermedium of claim 27 wherein the material capable of removingcharge-reducing contaminants comprises activated carbon.
 30. The filtermedium of claim 27 wherein the adsorbent material of said adsorbentlayer comprises an anion exchange resin.
 31. The filter medium of claim27 wherein said adsorbent prefilter further includes ingredientscomprising activated carbon, activated alumina, zeolites, diatomaceousearth, silicates, aluminosilicates, titanates, bone char, calciumhydroxyapatite, manganese oxides, iron oxides, magnesia, perlite, talc,polymeric particulates, clay, iodated resins, ion exchange resins,ceramics, or combinations thereof.
 32. The filter medium of claim 27wherein said microbiological interception enhancing agent consists of asilver-cationic material-halide complex wherein a homopolymer of diallyldimethyl ammonium on a surface of said microporous structure has ahalide counter ion associated therewith and wherein silver isprecipitated with at least a portion of the halide counter ion.
 33. Thefilter medium of claim 32 wherein the homopolymer of diallyl dimethylammonium halide has a molecular weight of greater than or equal to about400,000 Daltons.
 34. A filter system comprising: a granular bed ofparticles capable of removing charge-reducing contaminants; amicroporous structure, disposed downstream from said granular bed,having a mean flow path of less than about 0.6 micron; and amicrobiological interception enhancing agent comprising asilver-cationic material-halide complex having a high charge density,coated on, at least a portion of a surface of said microporousstructure.
 35. The filter system of claim 34 wherein the particlescomprise activated carbon.
 36. The filter system of claim 34 wherein theparticles comprise an anion exchange resin.
 37. The filter system ofclaim 34 wherein said granular bed of particles further includesingredients comprising activated carbon, activated alumina, zeolites,diatomaceous earth, silicates, aluminosilicates, titanates, bone char,calcium hydroxyapatite, manganese oxides, iron oxides, magnesia,perlite, talc, polymeric particulates, clay, iodated resins, ionexchange resins, ceramics, or combinations thereof.
 38. The filtersystem of claim 34 wherein said microbiological interception enhancingagent consists of a silver-cationic material-halide complex wherein ahomopolymer of diallyl dimethyl ammonium on a surface of saidmicroporous structure has a halide counter ion associated therewith andwherein silver is precipitated with at least a portion of the halidecounter ion.
 39. The filter medium of claim 38 wherein the homopolymerof diallyl dimethyl ammonium halide has a molecular weight of greaterthan or equal to about 400,000 Daltons.
 40. A filter system comprising:a solid composite block comprising a material capable of removingcharge-reducing contaminants; a microporous structure, disposeddownstream from said block, having a mean flow path of less than about2.0 microns; and a microbiological interception enhancing agentcomprising a silver-cationic material-halide complex having a highcharge density, coated on at least a portion of a surface of saidmicroporous structure.
 41. The filter system of claim 40 wherein saidsolid composite block comprises activated carbon.
 42. The filter systemof claim 40 wherein said solid composite block comprises an anionexchange resin.
 43. The filter system of claim 40 wherein said solidcomposite block further includes ingredients comprising activatedcarbon, activated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, orcombinations thereof.
 44. The filter system of claim 40 wherein saidmicrobiological interception enhancing agent consists of asilver-cationic material-halide complex wherein a homopolymer of diallyldimethyl ammonium on a surface of said microporous structure has ahalide counter ion associated therewith and wherein silver isprecipitated with at least a portion of the halide counter ion.
 45. Thefilter system of claim 44 wherein the homopolymer of diallyl dimethylammonium halide has a molecular weight of greater than or equal to about400,000 Daltons.
 46. A process of making a filter medium comprising thesteps of: providing a microporous structure having a mean flow path ofless than about 1 micron; and coating at least a portion of themicroporous structure with a microbiological interception enhancingagent, the microbiological interception enhancing agent comprising acationic metal complex capable of imparting a positive charge on atleast a portion of the microporous structure.
 47. The process of claim46 wherein the step of providing a microporous structure comprisesforming a plurality of nanofibers having a fiber diameter of less thanabout 1000 nanometers into the microporous structure.
 48. The process ofclaim 47 wherein the step of providing a microporous structure comprisesforming a plurality of nanofibers, wherein at least a portion of thenanofibers are fibrillated into the microporous structure.
 49. Theprocess of claim 47 wherein the step of providing a microporousstructure comprises forming a plurality of nanofibers, wherein thenanofibers comprise organic fibers, inorganic fibers, or a mixturethereof, into the microporous structure.
 50. The process of claim 47wherein the step of providing a microporous structure comprises forminga plurality of glass fibers into the microporous structure.
 51. Theprocess of claim 47 wherein the step of providing a microporousstructure comprises forming a plurality of polymer fibers into themicroporous structure.
 52. The process of claim 51 wherein the step ofproviding a microporous structure comprises forming a plurality ofpolymer fibers wherein at least a portion of the polymer fibers aresubstantially fibrillated into the microporous structure.
 53. Theprocess of claim 47 wherein the step of providing a microporousstructure comprises forming a plurality of cellulose fibers into themicroporous structure.
 54. The process of claim 53 wherein the step ofproviding a microporous structure comprises forming a plurality ofcellulose fibers wherein least a portion of the cellulose fibers aresubstantially fibrillated, into the microporous structure.
 55. Theprocess of claim 47 wherein the step of providing a microporousstructure comprises forming a plurality of substantially fibrillatedlyocell fibers into the microporous structure.
 56. The process of claim55 wherein the step of providing a plurality of substantiallyfibrillated lyocell fibers comprises forming a plurality ofsubstantially fibrillated lyocell fibers wherein at least a portion ofthe fibrillated lyocell fibers are about 1 millimeter to about 8millimeters in length having a diameter of about 250 nanometers, intothe microporous structure.
 57. The process of claim 56 wherein the stepof providing a plurality of substantially fibrillated lyocell fiberscomprises forming a plurality of substantially fibrillated lyocellfibers having a Canadian Standard Freeness of less than or equal toabout 100, into the microporous structure.
 58. The process of claim 56wherein the step of providing a plurality of substantially fibrillatedlyocell fibers comprises forming a plurality of substantiallyfibrillated lyocell fibers having a Canadian Standard Freeness of lessthan or equal to about 45, into the microporous structure.
 59. Theprocess of claim 47 wherein the step of providing a microporousstructure comprises providing a membrane comprising an organic material,an inorganic material, or a mixture thereof.
 60. The process of claim 48wherein the step of providing a membrane comprises providing a polymermembrane.
 61. The process of claim 47 wherein the step of providing amicroporous structure includes incorporating into the microporousstructure one or more ingredients selected from the group consisting ofactivated carbon, activated alumina, zeolites, diatomaceous earth,silicates, aluminosilicates, titanates, bone char, calciumhydroxyapatite, manganese oxides, iron oxides, magnesia, perlite, talc,polymeric particulates, clay, iodated resins, ion exchange resins,ceramics, and combinations thereof.
 62. The process of claim 47 whereinthe step of coating comprises treating at least a portion of themicroporous structure with a cationic material having a counter ionassociated therewith to form a cationically charged microporousstructure; exposing the cationically charged microporous structure to abiologically active metal salt; and precipitating a biologically-activemetal complex with at least a portion of the counter ion associated withthe cationic material on at least a portion of the microporousstructure.
 63. The process of claim 62 wherein the step of treating atleast a portion of the microporous structure with a cationic materialhaving a counter ion associated therewith, the cationic material isselected from the group consisting of amines, amides, quaternaryammonium salts, imides, benzalkonium compounds, biguanides, pyrrolesaminosilicon compounds, polymers thereof, and combinations thereof. 64.The process of claim 62 wherein in the step of exposing the cationicallycharged microporous structure to a biologically active metal salt, thebiologically active metal is selected from the group consisting ofsilver, copper, zinc, cadmium, mercury, antimony, gold, aluminum,platinum, palladium, and combinations thereof.
 65. The process of claim64 wherein the step of precipitating a biologically-active metal complexcomprises precipitating a metal-amine-halide complex.
 66. The process ofclaim 65 wherein the step of precipitating a metal-amine-halide complexcomprises precipitating a silver-amine-halide complex.
 67. The processof claim 47 further including the step of providing a prefilter capableof removing charge-reducing contaminants from an influent prior to theinfluent contacting the microporous structure.
 68. A process for makinga filter medium comprising the steps of: providing a plurality ofnanofibers; coating at least a portion of a surface of at least some ofthe plurality of nanofibers with a microbiological interceptionenhancing agent, the microbiological intercepting agent comprising acationic metal complex; and forming said fibers into a microporousstructure having a mean flow path of less than about 1 micron.
 69. Theprocess of claim 68 wherein the step of providing a plurality ofnanofibers, the nanofibers are made from a material selected from thegroup consisting of polymers, ion-exchange resins, engineered resins,ceramics, cellulose, rayon, wool, silk, glass, metal, litanatesactivated alumina, ceramics activated carbon, silica, zeolites,diatomaceous earth, activated bauxite, fuller's earth, calciumhydroxyapatite, and combinations thereof.
 70. The process of claim 68wherein the step of providing a plurality of nanofibers comprisesforming a plurality of nanofibers comprising organic fibers, inorganicfibers, or a mixture thereof, into the microporous structure.
 71. Theprocess of claim 68 wherein the step of providing a plurality ofnanofibers comprises forming a plurality of fibrillated lyocell fibersinto the microporous structure.
 72. The process of claim 68 wherein thestep of providing a plurality of nanofibers comprises forming aplurality of nanofibers wherein a significant portion of the fibers areabout 1 millimeter to about 8 millimeters in length having a diameter ofless than or equal to about 1000 nanometers into the microporousstructure.
 73. The process of claim 68 wherein the step of providing aplurality of nanofibers comprises providing a plurality of nanofibershaving a Canadian Standard Freeness of less than or equal to about 100into the microporous structure.
 74. The process of claim 68 wherein thestep of providing a plurality of nanofibers comprises providing aplurality of nanofibers having a Canadian Standard Freeness of less thanor equal to about 45 into the microporous structure.
 75. The process ofclaim 68 wherein the step of providing a microporous structure includesproviding one or more ingredients selected from the group consisting ofactivated carbon, activated alumina, zeolites, diatomaceous earth,silicates, aluminosilicates, titanates, bone char, calciumhydroxyapatite, manganese oxides, iron oxides, magnesia, perlite, talc,polymeric particulates, clay, iodated resins, ion exchange resins,ceramics, and combinations thereof.
 76. The process of claim 68 whereinthe step of coating comprises treating at least a portion of surface ofat least some of the plurality of nanofibers with a cationic materialhaving a counter ion associated therewith to form a cationically chargedfiber material; exposing the cationically charged fiber material to abiologically active metal salt; and precipitating a cationic metalcomplex with at least a portion of the counter ion associated with thecationic material on at least a portion of the surface of at least someof the plurality of nanofibers.
 77. The process of claim 76 wherein inthe step of treating at least a portion of a surface of at least some ofthe plurality of nanofibers with a cationic material having a counterion associated therewith, the cationic material is selected from thegroup consisting of pyrroles, amines, amides, quaternary ammonium salts,imides, benzalkonium compounds, biguanides, aminosilicon compounds,polymers thereof, and combinations thereof.
 78. The process of claim 76wherein in the step of treating at least a portion of a surface of atleast some of the plurality of nanofibers with a cationic material, thecationic material comprises a homopolymer of diallyl dimethyl ammoniumhalide.
 79. The process of claim 76 wherein in the step of exposing thecationically charged fiber material to a biologically active metal salt,the biologically active metal is selected from the group consisting ofsilver, copper, zinc, cadmium, mercury, antimony, gold, aluminum,platinum, palladium, and combinations thereof.
 80. The process of claim68 further including the step of providing an adsorbent prefiltercapable of removing charge-reducing contaminants from an influent priorto the influent contacting the microporous structure.
 81. The process ofclaim 68 wherein the step of forming the microporous structure comprisesa wet laid process.
 82. A process for making a filter medium comprisingthe steps of: providing a plurality of polymer nanofibers; coating atleast a portion of a surface of at least some of the plurality ofpolymer nanofibers with a microbiological interception enhancing agent,the microbiological intercepting agent comprising a cationic metalcomplex; and forming a microporous structure having a mean flow path ofless than about 1 micron.
 83. The process of claim 82 wherein the stepof providing a plurality of polymer nanofibers, the polymer nanofibersare fibrillated.
 84. The process of claim 82 wherein the step ofproviding a plurality of nanofibers includes providing ingredientsselected from the group consisting of activated carbon, activatedalumina, zeolites, diatomaceous earth, silicates, aluminosilicates,titanates, bone char, calcium hydroxyapatite, manganese oxides, ironoxides, magnesia, perlite, talc, polymeric particulates, clay, 6 iodatedresins, ion exchange resins, ceramics, and combinations thereof.
 85. Theprocess of claim 82 wherein the step of coating comprises: treating atleast a portion of surface of at least some of the plurality of polymernanofibers with a cationic material having a counter ion associatedtherewith to form a cationically charged fiber material; exposing thecationically charged fiber material to a biologically active metal salt;and precipitating a biologically-active metal complex with at least aportion of the counter ion associated with the cationic material on atleast a portion of the surface of at least some of the plurality ofpolymer nanofibers.
 86. The process of claim 85 wherein in the step oftreating at least a portion of a surface of at least some of theplurality of polymer nanofibers with a cationic material having acounter ion associated therewith, the cationic material is selected fromthe group consisting of pyrroles, amines, amides, quaternary ammoniumsalts, imides, benzalkonium compounds, biguanides, aminosiliconcompounds, polymers thereof, and combinations thereof.
 87. The processof claim 86 wherein in the step of treating at least a portion of asurface of at least some of the plurality of polymer nanofibers with acationic material comprising of a homopolymer of diallyl dimethylammonium halide.
 88. The process of claim 85 wherein in the step ofexposing the cationically charged fiber material to a biologicallyactive metal salt, the biologically active metal is selected from thegroup consisting of silver, copper, zinc, cadmium, mercury, antimony,gold, aluminum, platinum, palladium, and combinations thereof.
 89. Theprocess of claim 85 wherein the step of precipitating a metal-cationicmaterial-counter-ion complex comprises precipitating asilver-amine-halide complex.
 90. The process of claim 82 furtherincluding the step of providing an adsorbent prefilter capable ofremoving charge-reducing contaminants from an influent prior to theinfluent contacting the microporous structure.
 91. The process of claim82 wherein the step of forming the microporous structure comprises a wetlaid process.
 92. The process of claim 82 wherein the step of formingthe microporous structure comprises a dry laid melt blown, spun-bondingor similar process.
 93. A process for making a filter medium comprisingthe steps of: providing a plurality of cellulose nanofibers; coating atleast a portion of a surface of at least some of the plurality ofcellulose fibers with a microbiological interception enhancing agent,the microbiological intercepting agent comprising a cationic metalcomplex; and forming a microporous structure having a mean flow path ofless than about 1 micron.
 94. The process of claim 93 wherein the stepof providing a plurality of cellulose nanofibers comprises forming aplurality of fibrillated lyocell fibers into the microporous structure.95. The process of claim 93 wherein the step of providing a plurality ofcellulose nanofibers comprises forming a plurality of cellulose fiberswherein a significant portion of the fibers are about 1 millimeter toabout 8 millimeters in length having a diameter of less than or equal toabout 1000 nanometers, into the microporous structure.
 96. The processof claim 193 wherein the step of providing a plurality of cellulosenanofibers comprises forming a plurality of cellulose nanofibers havinga Canadian Standard Freeness of less than or equal to about 45 into themicroporous structure.
 97. The process of claim 93 wherein the step ofproviding a plurality of cellulose nanofibers includes providingadditives selected from the group consisting of activated carbon,activated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, andcombinations thereof.
 98. The process of claim 93 wherein the step ofcoating comprises treating at least a portion of a surface of at leastsome of the plurality of cellulose nanofibers with a cationic materialhaving a counter ion associated therewith to form a cationically chargedfiber material; exposing the cationically charged fiber material to abiologically active metal salt; and precipitating a biologically-activemetal complex with at least a portion of the counter ion associated withthe cationic material on at least a portion of the surface of at leastsome of the plurality of cellulose nanofibers.
 99. The process of claim98 wherein in the step of treating at least a portion of a surface of atleast some of the plurality of cellulose nanofibers with a cationicmaterial having a counter ion associated therewith, the cationicmaterial is selected from the group consisting of pyrroles, amines,amides, quaternary ammonium salts, imides, benzalkonium compounds,biguanides, aminosilicon compounds, polymers thereof, and combinationsthereof.
 100. The process of claim 99 wherein in the step of treating atleast a portion of a surface of at least some of the plurality ofcellulose nanofibers with a cationic material having a counter ionassociated therewith, the cationic material comprising of a homopolymerof diallyl dimethyl ammonium halide.
 101. The process of claim 98wherein in the step of exposing the cationically charged fiber materialto a biologically active metal, the biologically active metal isselected from the group consisting of silver, copper, zinc, cadmium,mercury, antimony, gold, aluminum, platinum, palladium, and combinationsthereof.
 102. The process of claim 101 wherein the step of precipitatinga metal-cationic material-halide complex comprises precipitating asilver-amine-halide complex.
 103. The process of claim 93 furtherincluding the step of providing an adsorbent prefilter capable ofremoving charge-reducing contaminants from an influent prior to theinfluent contacting the microporous structure.
 104. The process of claim93 wherein the step of forming the microporous structure comprises a wetlaid process.
 105. A process of making a filter medium comprising thesteps of: providing a membrane having a mean flow path of less thanabout 1 micron; and coating at least a portion of the membrane with amicrobiological interception enhancing agent, the microbiologicalinterception enhancing agent comprising a cationic metal complex capableof imparting a positive charge on at least a portion of the membrane.106. The process of claim 105 wherein the step of coating comprisestreating at least a portion of the membrane with a cationic materialhaving a counter ion associated therewith to form a cationically chargedmembrane; exposing the cationically charged membrane to a biologicallyactive metal salt; and precipitating a biologically-active metal complexwith at least a portion of the counter ion associated with the cationicmaterial on at least a portion of the membrane.
 107. The process ofclaim 106 wherein in the step of exposing the cationically chargedmembrane to a biologically active metal, the biologically active metalis selected from the group consisting of silver, copper, zinc, cadmium,mercury, antimony, gold, aluminum, platinum, palladium, and combinationsthereof.
 108. The process of claim 106 wherein the step of precipitatinga metal-amine-halide complex comprises precipitating asilver-amine-halide complex.
 109. The process of claim 105 furtherincluding the step of providing an adsorbent prefilter capable ofremoving charge-reducing contaminants from an influent prior to theinfluent contacting the membrane.
 110. A process for making a filtermedium comprising the steps of: providing a plurality of nanofibers;coating at least a portion of a surface of at least some of theplurality of said nanofibers with a microbiological interceptionenhancing agent, the microbiological intercepting agent comprising asilver-amine-halide complex having a medium to high charge density and amolecular weight greater than 5000 Daltons; and forming a microporousstructure having a mean flow path of less than or about 0.6 microns.providing an adsorbent prefilter comprising a material capable ofremoving charge-reducing contaminants from an influent, and placing saidadsorbent prefilter upstream of said microporous structure.
 111. Theprocess of claim 110 wherein in the step of providing an adsorbentprefilter; the material of the adsorbent prefilter comprises a materialselected from the group consisting of activated carbon, activatedalumina, zeolites, diatomaceous earth, silicates, aluminosilicates,titanates, bone char, calcium hydroxyapatite, manganese oxides, ironoxides, magnesia, perlite, talc, polymeric particulates, clay, iodatedresins, ion exchange resins, ceramics, and combinations thereof. 112.The process of claim 110 wherein in the step of providing an adsorbentprefilter, at least a portion of the material of the adsorbent prefilterhas formed thereon a microbiological interception enhancing agent. 113.The process of claim 110 wherein the step of providing a microporousstructure includes providing a binder.
 114. The process of claim 110wherein the step of providing a microporous structure includes providingadditives selected from the group consisting of activated carbon,activated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, andcombinations thereof.
 115. The process of claim 110 wherein the step ofcoating comprises treating at least a portion of a surface of at leastsome of the plurality of nanofibers with a quaternary ammonium salt toform a cationically charged fiber material; exposing the cationicallycharged fiber material to a silver salt; and precipitating the silverwith at least a portion of a halide counter ion associated with thequaternary ammonium salt on at least a portion of the surface of atleast some of the plurality of said nanofibers.
 116. The process ofclaim 115 wherein in the step of treating at least a portion of asurface of at least some of the plurality of nanofibers with aquaternary ammonium salt, the quaternary ammonium salt comprises ahomopolymer of diallyl dimethyl ammonium halide.
 117. The process ofclaim 110 wherein the step of forming the microporous structurecomprises a wet laid process.
 118. A process for making a filter systemcomprising the steps of: providing an adsorbent prefilter comprising amaterial capable of removing charge-reducing contaminants from aninfluent, wherein the material is immobilized into a solid compositeblock; providing a plurality of nanofibers; coating at least a portionof a surface of at least some of the plurality of said nanofibers with amicrobiological interception enhancing agent, the microbiologicalintercepting agent comprising a silver-amine-halide complex having amedium to high charge density and a molecular weight greater than 5000Daltons; and forming a microporous structure having a mean flow path ofless than or about 0.6 microns.
 119. The process of claim 118 wherein inthe step of providing an adsorbent prefilter; the material of theadsorbent prefilter is selected from the group consisting of activatedcarbon, activated alumina, zeolites, diatomaceous earth, silicates,aluminosilicates, titanates, bone char, calcium hydroxyapatite,manganese oxides, iron oxides, magnesia, perlite, talc, polymericparticulates, clay, iodated resins, ion exchange resins, ceramics, andcombinations thereof.
 120. The process of claim 118 wherein the step ofproviding a plurality of said nanofibers includes providing additivesselected from the group consisting of activated carbon, activatedalumina, zeolites, diatomaceous earth, silicates, aluminosilicates,titanates, bone char, calcium hydroxyapatite, manganese oxides, ironoxides, magnesia, perlite, talc, polymeric particulates, clay, iodatedresins, ion exchange resins, ceramics, and combinations thereof. 121.The process of claim 118 wherein in the step of providing an adsorbentprefilter, at least a portion of the material of the adsorbent prefilterhas formed thereon a microbiological interception enhancing agent. 122.The process of claim 118 wherein the step of coating comprises treatingat least a portion of a surface of at least some of the plurality ofsaid nanofibers with a quaternary ammonium salt to form a cationicallycharged fiber material; exposing the cationically charged fiber materialto a silver salt; and precipitating a silver-halide complex with atleast a portion of the halide counter ion associated with the quaternaryammonium salt on at least a portion of the surface of at least some ofthe plurality of said nanofibers.
 123. The process of claim 122 whereinin the step of treating at least a portion of a surface of at least someof the plurality of said nanofibers with a quaternary ammonium salt, thequaternary ammonium salt comprises a homopolymer of diallyl dimethylammonium halide.
 124. The process of claim 118 wherein the step offorming the microporous structure comprises a wet laid process.
 125. Amethod of removing microbiological contaminants in a fluid comprisingthe steps of: providing a filter medium having a microporous structurehaving a mean flow path of less than about 1 micron, the microporousstructure having coated on at least a portion thereof a microbiologicalinterception enhancing agent comprising a cationic metal complex whereinsaid cationic material has a medium to high charge density and amolecular weight greater than about 5000 Daltons; contacting the fluidto the filter medium for greater than about 3 seconds; and obtaining atleast about 6 log reduction of microbiological contaminants smaller thanthe mean flow path of the filter medium that pass through the filtermedium.
 126. The method of claim 125 wherein the step of providing afilter medium comprises providing a filter medium wherein themicroporous structure comprises a plurality of nanofibers such that themicroporous structure has a mean flow path of less than about0.6.microns.
 127. The method of claim 125 wherein the step of providinga filter medium comprises providing a filter medium wherein themicroporous structure comprises a plurality of fibrillated lyocellfibers such that the microporous structure has a mean flow path of lessthan about 0.6 microns.
 128. The method of claim 125 wherein the step ofproviding a filter medium comprises providing a filter medium whereinthe microporous structure comprises a membrane such that the microporousstructure has a mean flow path of less than about 0.6 microns.
 129. Themethod of claim 125 wherein in the step of providing a filter medium,the microbiological interception enhancing agent is coated by: treatingat least a portion of the microporous structure with a quaternaryammonium salt to form a cationically charged microporous structure;exposing the cationically charged microporous structure to abiologically active metal salt; and precipitating biologically-activemetal with at least a portion of a counter ion associated with thequaternary ammonium salt on at least a portion of the microporousstructure.
 130. The method of claim 125 wherein in the step of providinga filter medium, the microbiological interception enhancing agentcomprises a cationic polymer having a medium to high charge density anda molecular weight of about 400,000 Daltons, and a biologically-activemetal is precipitated with at least a portion of the counter ionassociated with the cationic polymer.
 131. A gravity-flow filtrationsystem for treating, storing, and dispensing fluids comprising: a firstreservoir for holding a fluid to be filtered; a filter medium in fluidcommunication with said first reservoir, said filter medium comprising amicroporous structure with a mean flow path of less than about 1 micron,and wherein said filter medium is so treated as to provide at leastabout 4 log reduction of microbiological contaminants smaller than themean flow path of said filter medium; and a second reservoir in fluidcommunication with said filter medium for collecting a filtered fluid.132. The gravity-flow filtration system of claim 131 wherein said filtermedium has a volume of less than about 500 cm³ and has an initial flowrate of greater than about 25 ml/minute.